"Switching between 3d modellers" undersells the issue.
COMPLETELY ALTERING YOUR PRODUCTION PIPELINE TO ACCOMMODATE ONE PACKAGE gets the point across a little bit better.
There are studios out there that have decades of in-house scripts and programs built around a given set of software. If you do a lot of architectural rendering you may have your own outdoor lighting systems. If you focus primarily on title sequences you may have certain effects that you developed. Having to completely rewrite all of that in-house code would be a MASSIVE undertaking.
I don’t think the popularity of proprietary solutions is vanity, it’s rather that switching between 3d modellers is really hard. It might be months before you’re even close to productive again. Also interoperability between packages is a huge problem. Blender only really started to get a good UI this decade, and I think you’re more likely to see it get picked up in new shops rather than old shops migrating.