If you are a bank, you issue loans only on things that are likely to have a positive ROI. With a mortgage, you know what the property is worth and can foreclose on it if the borrower isn't able to make the payments.
No such equivalent with a college student. 18-year olds for the most part aren't going to know for sure what they want to major in, so "a useful degree" at the time the loan is signed, might change 2 years in, when they actually have to declare a major.
We can easily conceive of loans that are contingent on the major not changing to something useless. I don’t believe flaws in the current system have to stick forever.
