Because of tradition. Ages ago Macs were vastly superior to PCs when it came to audio/video/graphiocs work. That’s why “everybody” used them and all the new guys in the industry learned things with Macs and passed their knowledge to the next generation and the next and…
While PCs have performance advantage nowadays, it’s pointless to switch and learn new system just to get that tiny extra performance.
Of course there are also die-hard Mac cheerleaders who continue to shout out the old slogans of the 1990s, like: “Macs are faster, Macs are better, PCs crash all the time”. These were true back then but not anymore and for some people it’s hard to accept the fact that world has changed. But most of the Mac users just use the system they are familiar with. If it ain’t broken, don’t fix it.