Not every DM loves a page worth of backstory, but I do...

[Tawmis]

But, as much as I dislike AI, I also hate writing backstories. I always have, especially when I was young and all the roleplay I did was on free-form RP forums. I hate trying to fit a still-nebulous idea of a character into a socially expected amount of paragraphs or pages. Were I a less scrupulous individual, I might very well use AI to vomit something onto my character, simply to fill the space.

Which is totally fair. I get not everyone (maybe even most?) don't enjoy writing backstories.
For me, that's always given me a feel for the character - to flesh it out, beyond the Bonds, Flaws, etc., that can be selected during character creation.
Why do I have the flaws that I have? What makes me want to ensure I protect my friends at all costs?

For example, I am currently playing in a "Delta Green" (https://www.delta-green.com/) - I'd never played (or even heard of) this game until a month ago. But it's essentially X-Files meets Cthulhu (with character deaths and insanity a common place). My first character died (no shocker) by the second session. No shocker, but also, no loss. I didn't care that he died. Rolled up a second character, and he's survived now a few sessions - so on my own, I wrote a backstory for him (based on his profession, his bonds, and how he got into Delta Green, what he found that interested them). Now, as I am playing him in the game, I definitely care more about him - but I also get way more into character with him (he's very, very, very, very close to going utterly insane when we ended the last session), but I've enjoyed playing that up.

Now everyone may not be a psycho and need that extra story bit to really feel like they're stepping into their character.

I guess it's all about expectations. I don't expect my players to make a long or detailed backstory (I'm fine with a few phrases, or just a general vibe), so there isn't that pressure to use AI in order to make something that's up to my standards. I'm sure you don't have huge requirements of your players in that regard, either, yet by putting a significant amount of focus on that aspect of their characters, it's not hard for a perceived necessity of "detailed backstory" to be constructed, even if it is an erroneous perspective. Apologies if you've already considered this point, though.

Oh, I never expect my players to do it, either. I've always enjoyed doing it - and they've told me it's helped them (same idea, I mentioned - adding the depth to step into that character's personality and leave their own behind during the game).

Beyond what Unoriginal said ...
With the former, I look at the player and say "give me three to five sentences, in your own words, on why you are an adventurer. Put yourself in your character's shoes and do that.
If you can't put forth that much effort, why should I put effort into building and running a world for you?
Help me out here. I need it to come from you, since you are the one playing in our game...and it's you that I want to work with and play with for this game...you, not some soulless algorithm.
And if you want to give me some more later, as you get to know your character better through play, we can add to it ... "

And that makes sense. Again, not everyone is a psycho like me. :D

What's been fun - so, one of my regular players - his wife, and her two brothers (and his own brother) have all wanted to play D&D. They've heard (one side) of the conversation often when he's been playing - and so I said I'd run a game for them. Now rather than use my own homebrew world - I knew they're all familiar with the Dragonlance novels (especially Chronicles, the first trilogy). So I wove an adventure around the same time frame as the first book (but taking place in a different area of Ansalon, the main continent) - and it was supposed to be a one shot (but the psycho I am, wrote an adventure that's already 53 pages long, in case - with my hope, it'd go beyond that first session). So they all created characters on D&D Beyond through my campaign I made - I went into their characters, created backstories that tied to the campaign I had written (tying some people to NPCs I knew would be in the adventure and such). And they were all really surprised by the first session, and how much they enjoyed it - so now we got a monthly game going.

I don't care what tools someone uses, as long as they know and agree with what they're handing me - and agree that what they're handing me is what they want to play. If someone has a few ideas but isn't good at connecting them and wants to use ChatGPT to do that work, its fine, as long as they've actually read what comes out and are interested in playing that character. What would be bad would be if a player assumed that I was trying to assign them homework or get them to prove their commitment to the campaign or something, generated a bunch of stuff, didn't bother to read it closely, and handed it to me as 'here, assignment done'. If e.g. I then make reference to something in that backstory and they're like 'huh?' or RP totally differently than their backstory suggested for their motivations or relationships, then that's worse than if they just didn't hand me anything.

True, but hopefully your players read what they kick out (even if using ChatGPT), even if it's just a page long. :) If they don't have the attention span for that, I would question if they have the attention span for a long adventure or waiting for you to finish describing the scenery around them without shouting, "I just attack them!" :D

For me the point of the backstory is player engagement, so when backstory tie ins come up if the player is engaged I don't really care if they wrote it themselves. I don't see much difference between using AI or coming to a forum like this and asking for a backstory.

And that is a fair point (ChatGPT vs going to a forum) - except going to a forum, at least it's another human helping you out. lol

I'll work with whatever backstory I'm given, but my only requirement on my players is that they can explain why this character is in this dangerous line of work. They can give me as much as they want as long as they can answer that question. I've gotten everything from a single line to a full page. I engage with the players who are engaged, I work with the players who want to deepen their engagement, and I let the players who want to be on the world but not really in it have their fun.

I do the same - some players are there to "pew pew pew" everything, some are there for the social, some are there to do the most damage; I try to accommodate for everyone at the table. In one example, one of my players is a huge fan of Dragonlance (see above) - and their character is pretty much designed very close to Tanis (if you're familiar). So the background I wrote for him using his flaws, traits, etc., I intentionally made to mimic closely to Tanis. So when the ex-girlfriend comes calling on her blue dragon, there was a chance for some RP and discover what she's been up to, why she's riding a blue dragon, etc. The player didn't bite, so that whole segment was pretty much cut very short, and she's not surfaced again (I had plans if he did partake, but since that wasn't his cup of tea, that story went out the door, no harm, no foul).

On the other hand, if you're setting up a game that's like "we're just gonna run a different oneshot every week, don't expect to play the same character twice," it's a lot more understandable that someone might want to phone it in some weeks. But that format also probably doesn't require more than one or two points of characterization anyway.
So overall, the legitimate use cases are narrow, but I am also not that unsympathetic to players who would do this, because (again) I know people who are those people that roleplay well but have a rough time sitting down and writing. I would rather more people play D&D, not fewer.

Yes, for Oneshots - yeah, there's no need for fleshed out backgrounds (unless they want to). For example, above I mentioned the Delta Green I am in; literally each one can be a one shot (because your character may die or go insane in one session). So my first character, I didn't bother - and he died. lol Second character, after he survived more than one session, I took it on myself to write a backstory, never sure if it's the next session he's gonna die or go insane. But not everyone is the psycho that I am. :D