> Because they're bloody good (well, Photoshop is). And Gimp isn't.
Imagine you're teaching people carpentry. There is a really nice automatic screw gun that accepts a cartridge of screws all lined up automatically so each one loads in place after the last one. It is super easy to use and people can get straight to fastening beams together. But the device is very expensive, and they cannot be repaired if they break, and the screw cartridges require a monthly plan where they will send you screws even if you still have plenty from last month, with a chip to make sure the screws won't feed from last month.
Now compared to a boring battery operated drill, where the user has to gasp place each screw on the drill bit by hand, these fancy automatic screw feeding drills seem WAY BETTER! Surely the person can make better buildings with the fancy screw gun right? And we want them to make the best buildings possible right?
Well the boring drill has user serviceable parts. Everything can be removed and replaced if needed. There are no control chips to stop it working. You don't have to pay every month for anything. And placing each screw on the bit by hand is fine, it's what everyone did ten years ago and those buildings are all still standing. Heck you're standing in one of those buildings right now!
So maybe we should teach the students how to use tools that work without all this extra cost and nonsense. It's really a minor difference, since the point isn't to use the fanciest possible tool, but to teach them how to build buildings in a way that they can always take with them everywhere they go. And after they graduate school, they're not going to want to pay every month for one of those fancy drills!