Do caster out of combat options matter?

[Unoriginal]

Not really. A character with Plane Shift run by a player who intends to use the spell is likely to have already have tried sourcing some tuning forks, much more likely to have a 14+ int and appropriate knowledge proficencies, and almost certainly has divination spells that can help.

Which divination spells are you saying will help with that task?

Locate Object doesn't have that big a range, and that's the only relevant spell I can think of.

They may be in a great position to ask the GM what their character knows, cast a few divinations, and have or already know how to get the tuning fork.

Indeed. And that is a DM intervention.

If the GM OKs the planar travel but doesn't like portals, is using a setting without them, or us using a setting where they aren't conveniently located, then the non-casters get a nope or the GM has a lot of work to do. Whether or not those things are true the caster has a faster, easier, and rules enabled method to do the same thing that will be less work and less intervention for the GM unless they decide to make a big involved quest out of getting the tuning fork.

If the GM OKs the planar travel but doesn't like Plane Shift, is using a setting without it, or is using a setting where tuning forks aren't conveniently located, then the casters get a nope or the GM has a lot of work to do.

That's what I mean when I say both requires DM intervention.

Again, it is true that "we need to find a portal" is a very different dynamic/plot line than "I have a spell that can do the job". But that doesn't make one less DM-interventiony.