I'm pretty sure it's because just about every applicable art school has enforced their student's output to be done in adobe's products - meaning that Adobe has a firm grip on the educator's market. As the saying goes, hook them in when they're young and they'll be too lazy and vested to move away from their products for a lifetime.
The problem is that Adobe still makes the best tools in a lot of categories.
They also have the whole ecosystem lock-in model that also worked for Apple: their products work together, so if you try to replace Photoshop, you're probably still using Illustrator, and After Effects, etc. except your workflow isn't as smooth anymore, because there's one tool in the chain that works differently than the rest.
To a degree, Oracle was doing the same thing. Years ago I was teaching Data Science courses at the local Uni and Dean pulled me in and asked me if I can teach Introductory course in Web Dev, the current teacher was going on maternity leave. I was like heck yea, LFG. Student reaches out to me few days before the quarter was to start and asks if they need to buy the book since it is $285 (like $500 in today’s dollars). I was taken aback and went to my office and book was actually at my desk, “web development with oracle forms” … :) that was the course that was thought… (I didn’t of course - that was the last quarter I was asked :) )
And on top of that, if your clients are Adobe users, you probably will have to be as well or you risk what they send you not opening properly.
Back in the Creative Suite days, my parents (small graphic design studio) upgraded largely because a client upgraded and they needed to be compatible with the newer version of the file format. Creative Cloud "fixed" that, I guess.
It's been some time since I checked in on student related stuff, but..
IIRC PSDs contain some process related information that instructors check on; like for example photoshop layering contributes to file sizes and they don't want their students abusing it to the point of large file sizes; it'd look bad for their school's reputation.
