People who make up to 125K are eligible, but roughly 90% of the 43m people who took those loans are lower to middle class. 90% of 43m is roughly 40m; I wasn't counting the estimated 10% who are already up there.
Because a) they invested in their own education, and having more people with higher education benefits the whole society, and b) unlike home, business, or even car loans, most of these massive loans were taken people when they were very young, and didn't necessarily have the knowledge of how to plan their own finances or c) don't now have the ability to pay it back ; and d) an awful lot of the lenders are shady, borderline predatory. That's off the top of my head.
If you think about it in terms of society as a whole, rather than trying to think of its effects toward one single person, it makes a lot more sense.