I mean, the economy in 3.5 is super broken, presumably to facilitate an environment where people feel like going out and beating up zombies or whatever is a better way to make a living than, for example, running a business.
More generally, not every genre is equally equipped to tell every story, and BG3 isnt really about the personal identity of any of the origins except Durge (who, being customizable, could well be trans if you wanted).
ETA: I want to be clear here, i'm not saying they couldnt have done it. Theres absolutely a version of BG3 where "who are you" are the arc words and not just something clever at character selection. I'm saying their choice not to is just as legitimate as it would have been to have done so.
ETA 2: Also, hot take, Karlach would make a better trans character than Gale.