SGI made a few NT computers as an attempt to sell PCs which of course didn't work out due to not offering much except for a name an inflated price. Linux was coming around at the time, but SGI wouldn't have been an early adopter of Linux by any means since Irix was one of the jewels of the company, and helping adoption of Linux would have helped people transition to commodity PCs.

NT was a part of the transition for much smaller groups or individuals since they could buy a dual processor pentium II/pro and put a decent amount of RAM in them along with an Oxygen card that would accelerate OpenGL.

Large studios had a huge amount of infrastructure built up in pipeline scripts and workflow, proprietary software that might have used POSIX APIs and GUI libraries that weren't on windows, and big network file systems that tied things together.