Big, and even mid/small studios are like steering aircraft carriers, it takes a while, and you have to check every possible potential issue before you commit, and even then it has to go slow and careful. I don't think we transitioned to Maya till at least version 4 or later. I started back in Maya during it's Alpha/Beta stages while still making games in PowerAnimator because Maya just wasn't ready yet. It's not like the Maya 2-3-4 era anymore. Maya's updates are so incremental at this point, and studios tend to just write their own tools to make up for any shortcomings or project specific tools, that it almost doesn't matter. Most places I know have stopped at Maya 2022, or even Maya 2019 since there are so few new tools they need.

I know a few places that have dedicated teams just doing the tools transitions sitting off in another room, isolated trying to roll everything over, but it'll take a team a year or more to get everything working in Python3 before they 'flip the switch'. So many game/film studios have hundreds of tools written in Python2, that many are running Maya 2023 in Python2 mode because the tools changes are so daunting. The pipeline is the key factor, hell, Maya 2023 is having a bit of a hard go with the Python3 change. It's easier to write those features into Maya, and most studios (games/film), don't use vanilla Maya tools anyway. Maya may or may not be the best software, however, many of the big studios pipeline tools are still integrated into it and it's more work to change 20 years worth of tools than switch to another software for a few new features. Not to mention Motionbuilder integration. Maya is pretty much the standard, but even when not and something is proprietary, it's typically still built similar to Maya since it was king for so long.

Autodesk maya 3d animation