College is optional. Actually, if you're just looking for "a skilled job" trade school is a better bet than college now. But the only people actually saying that are conservative nut-jobs trying to fight a culture war against a balanced education. People send their kids to colleges for the same reason why they demand more car lanes instead of better buses and trains: it's a status symbol.

The thing about status symbols is that you are buying them to feel better than someone else. So they almost have to be scarce - and therefore expensive. That's the basic idea behind cost disease; scarce things in an economy of abundance become more expensive, not less.