Because game dev, at the best of times, is a giant multi-year gamble. You have to hope that people like the game you are in year 3 on because you don’t have money to go much past 4. And you also have to hope that another more popular studio doesn’t release something similar that cannibalizes your sales.
One way to make that safer? Get a publisher with deep pockets. Someone who can say “Hey, Elden Ring just came out and even has the same ‘there is a whole other world underground’ gimmick that you do. Can we delay your game for another six months but keep paying you the entire time?”
And those kinds of publishers tend to prefer the big studios where pivoting to a new engine or making a prototype for a radical genre shift is viable.
And this also applies to the insanely successful small studios. Dead Cells is a great example. Motion Twin is mostly a worker cooperative. This greatly limited its scalability (profit sharing for indie games doesn’t scale all that well) and resulted in a spin off of Evil Empire to manage Dead Cells.
Unionization will go a long way toward avoiding the worker abuse inherent in game dev. But startups are dangerous no matter what industry you are in.