Eh, I get it. As popular as the brand is, I can understand studios being hesitant to take the main cast on a new adventure, since it’s not very believable with what they already do.
There can be an appeal to a “just a nobody” story in the same universe, but then the only thing you can rely on is the setting and brand recognition.
A side character turned main character let’s you “expand the universe” with a known character, and nest something with the existing story, without feeling like beating a dead horse in a fan-fic-esque revisit of the main cast.
I was curious with Gollum, how they’d make an interesting game with an engaging story about a generally unlikeable side character.
Turns out they didn’t. But it probably would’ve been very impressive if they had!