It's not based on the whims of a company, it's usually based on what runs the software they need to run well, and what the operators like working with and how w

It's not based on the whims of a company, it's usually based on what runs the software they need to run well, and what the operators like working with and how well it integrates with the rest of the production line. The higher up in the food chain you get with production the less these machines are used as general purpose computing boxes and the more they just run one task (be it color grading, compositing, editing, sound editing & foley). Yes, you can use Windows/Linux PCs, and they make more sense for a lot of 3D work and certain other tasks but at the end of the day Apple macOS and hardware just make sense and the cost is not a problem.