It doesn't, but half of everybody has a sub-100 IQ. And a lot of the people taking on these loans (i.e. the students) are being guided by people (parents and professors) who have a really poor understanding of the job market. I can't tell you how many kids I've run across who think they're going to get some sort of audio gig on Indeed. If you graduate college thinking that, then you got cheated.
I don't think low IQ necessarily explains why people choose to embark on low-probability fields of study.
At least in my own experience, the people I know who've made that mistake are all very intelligent people. Well-read, very smart in an academic sense, and completely rational in almost every other part of their lives.
I'll use my cousin as an example. She's very intelligent, she went to Baldwin Wallace here in Northeast Ohio. It's considered to be a more "elite'ish school" (not quite Ivy League level, but certainly above a Cleveland State or Kent State). They have some fairly stringent entry requirements and I'd be highly shocked if you could find a single person going to school there with a < 100 IQ.
She still opted to go there and get her undergraduate degree in "Studio Art"...bunch of debt as a result. Needless to say, Northeast Ohio doesn't have a "thriving art scene".
I (and other family members) had that conversation with her on more than one occasion that what she wanted to do for a living was going to be a long shot (to no avail).
I don't think it comes from a place of ignorance or stupidity as much as a comes from a place of the "participation medal" generation, where kids end up with unrealistic expectations and think "I'm special, I know it's a long shot, but I'm going to be the one who makes it!"
She scored a 1520 on her SAT, so clearly she has a grasp on math and how to assess statistical probability based on data, but she's working at Target part time during the week, and works in one of Cleveland's few art galleries on the weekends for $18/hour (with huge debts to pay back) as a result of her decisions. So that just goes to show, even really smart people can have blind spots.
This notion that "because I'm really passionate about it, I deserve to make a lot of money doing it" is a problematic notion being instilled in younger generations.