I think at a certain point, you either value having your own skills and knowledge, or you don't. You may as well ask why anyone bothers learning to throw a baseball when they could just offload to a pitching machine.

And I get it. Pitchers who go pro get paid a lot and aren't allowed to use machines, so that's a hell of an incentive, but the vast majority of kids who ever pick up a baseball are never going to go pro, are never even going to try to go pro, and just enjoy playing the game.

It's fair to say many, if not most, students don't enjoy writing the way kids enjoy playing games, but at the same time, the point was mostly never mastering the five paragraph thesis format anyway. The point was learning to learn, about arbitrary topics, well enough to the point that you could write a reasonably well-argued paper about it. Even if a machine can do the writing for you, it can't do the learning for you. There's either value in having knowledge in your own brain or there isn't. If there isn't, then there never was, and AI didn't change that. You always could have paid or bullied the smarter kids into doing the work for you.