alt Hacker NewsI think it's that the biggies are focused on big budget AAA titles that they can sell for $70 or monetize as a FOMO live service, their distinguishing factor compared to indie games is high production values, and they don't feel like they have enough of an advantage in this space, or that they can get enough revenue to justify the huge expenditure of a AAA game.
Basically the same reason many other genres (e.g. roguelites) are dominated by little indie studios.
Plus the studios that have become AAA did it because they implemented interesting ideas, limited by their size constraints. The they get scale and lose the size constraints that caused the to go after interesting ideas.
The real successor to an old AAA series is the new series made by people who played it as kids.