Both Linux and Windows still take a _lot_ more maintenance than macOS. If you have a room full of creative video artists, who are not techies, then you want them to have maximum productive up-time. You do not want to have to employ a small army of system support techies to keep those boxes running.

I used to work on a PC magazine in the West End of London. The mag was about Windows PCs, and was written on Windows PCs, but it was laid out on Macs. I supported both, and the servers and the network.

The PC side of things needed more than 10x as much support.

That's not materially different even today.

Secondly, it's not just about the boxes and their OS. It's also about the apps. A lovely fast sleek Linux distro is no use at all if it doesn't run the apps you need... and if those apps only run on one vendor's kit, or even just run best on that vendor's kit, then that is the kit you buy.