I don't even understand how the notion of a "student loan bubble" makes sense, since people don't "speculate" on college like they speculate on real estate.
This is exactly what's going on. They're making the bet that they'll be in demand later and able to pay off their loans. Just like buying a house and being able to make money from it later. After all, everyone had a rationale as to why the price of their house would increase just like they do about the job market turning around for people with a degree/diploma in X.