It is expensive because it confers greatly enhanced earning potential. Students borrow against that future income. Sometimes from the state.
It confers enhanced future income largely because of the inherent vetting process that asures future employers this person is able to focus for extended periods of time on intellectual tasks, is able to follow through and function within a bureaucracy. I don't think it's as much about skills, at least it's way overkill for the skills that are actually needed on the job for most jobs.
I don't see the rise of LLMs as obviating the "functional cog in the Rube Goldberg machine" training.
This is just another way of saying that people go to school to buy access to the network, not for education itself.
It is also expensive because the debt is very hard to get erased through bankruptcy, so private companies are now offering more money to people than is actually needed. So universities see this $ and raise prices.
Kinda like how tax breaks on housing initially help people, and then the market adjusts based on the new inflow of $.