I've been out of school for ten years, and haven't used calculus in about twelve. How exactly do you think knowing calculus would have helped here? Be careful assuming everyone learned the subject as you did and knows how/when to apply it to various situations.
Personally, I learned about interest rates in middle school. I used that knowledge, combined with additional research on subsidized loans, to decide to take out loans. I also had the advantage of learning the downsides of debt collection from my brother's mistakes.
Not everyone is a rational economic actor. Children/young adults ages 17-22 definitely aren't the most rational amongst us.
You mean like the people who keep lending money to students who aren't going to be able able to pay it back?
(Somehow -- through mechanisms that are still beyond me -- this is exactly what happened in 2008. Absurd.)
Seriously though it's obviously by design. Ever wondered why they don't teach financial responsibility in school? Give people incentive to work as much as they can to keep economy rolling. Capitalism at it's finest.
When people take the loan it's because they feel like they have to, and when they don't want to repay it, sometimes it's like, "No, look: if the people around me needed this so that I could live, something's wrong, and I don't want to continue collaborating with them."
The U.S.A. may also be experiencing an ongoing violent revolt against compulsory literacy in the high schools, so the problems don't really start with the loans and the college application process.