Solasta: Crown of the Magister is a game with 5e ruleset that has done a pretty good job with a fraction of Larians budget.
This...doesn't answer the question I asked. You said "games." (And it actually was you, this time!) That's one successful game. Where is the at-least-one-more?
I'm not saying it isn't possible. Solasta shows it is (though I have my criticisms, I'll leave them out.) But you absolutely referred to games, plural, and made it sound like this was a common occurrence that Larian was foolishly and blatantly ignoring. There's only two 5e-based games I could find, one of which is defunct, the other did not start crowdfunding until several months
after Larian announced they were working on Baldur's Gate III. That is, the BG3 announcement happened June 2019, and they had begun working on the project as much as two years earlier (when Wizards contacted them asking if they were still interested in a licensing deal.) Solasta entered crowdfunding in
September 2019, went into Early Access in 2020, and was released in 2021. By the time the first (and, as far as I can tell,
only) successful 5e-based game had launched and proven its credentials, BG3 had been worked on to one extent or another for
at least two years, probably more like four.
There was no massive precedent for well-structured, "adapt the video game to the rules" games (to use Solasta's developers' own phrase), and there never really
has been a massive precedent. The only other "5e-based" game
flopped. When coupled with the extra expense and manpower that would be required for designing a whole new codebase from the ground up, and the fact that there simply weren't any such games to take inspiration from...
and the fact that it was WotC being impressed with DOS2 that got them the license in the first place...I really don't think you can argue that it was some utterly boneheaded self-indulgent move. I think it was pretty clearly the
only rational choice, and I would argue it remains a very rational choice today.
EDIT EDIT - They've also apparently said they've been considering holding some races back until full release. Personally I take this as "We're going to wait until the game releases to drop the bomb that there will be no Dragonborn in the game, even as NPCs", but perhaps I am too cynical.
As I argued earlier, it would be pretty weird to be "holding back" such races with the intent of declaring them cut later on, while at the same time actively adding fully-modeled heads for both genders, and actively recording
and coding in new voice lines specifically for them. It wouldn't be totally impossible, stranger things have happened, I recognize that. But it
would be odd to continue investing time and money into something they were already intending to drop. You could maybe argue that they already had the voice files, but why code them into the game when they weren't before? And why keep working on dragonborn heads if you don't actually want them in the game? Surely the time and effort spent on that would be better spent on half-orcs, which are near-human and thus shouldn't require nearly as much effort to implement.
It is quite disappointing to hear that there's so little character customization, and that even the stuff fans are hoping they'll add is pretty meager (seriously, decade-old games have better options than that!) I don't mean to treat this as sunshine and roses. It isn't. But the aforementioned new implemented NPC dialogue (and there's a fair bit of it, at least two different VAs making explicit references to dragonborn or the "blood of dragons" or the like)
and the already-rendered character heads seems reason enough to be (very) cautiously optimistic.