As someone who made similar choices and managed to avoid a quarter million dollar loan through sheer dumb luck, it's a variety of factors, some of which have to do with "the system" or "capitalism" (whatever that means) but most of them having to do with the fact that people are just idiots when it comes to this kind of thing.
When I was in high school (2004-2008), there was a huge stigma about going to college. It was the path to success, and the more expensive the school, the higher the quality of education. Now that I'm out (and OP is out, and lots of people are out) and people are sitting us down and asking "but why on earth did you think this was a good idea" and the answer is that from the time we were pretty much children, EVERYONE in our lives told us that it was not only a good idea, it was the only way to survive. Teachers, parents, guidance counselors, scout leaders, everyone you knew was telling you that there was one path to success, and it involved getting into the best college in the world. Anyone could work fast food or some trade, but everyone going to college would be running the show.
The other major factor is, most 18 year olds don't know what $100k means, and most of their parents/teachers don't bother to tell them. I sure as hell didn't know when I was 18. I remember asking my parents about the price tag and being told "you only live once and it's better to spend it being happy than worrying about money". I think when you're 18 it's also easier to figure "the price tag is 100k, I'll be making 30k, so therefore I can pay it back in under four years" because no one tells you about the cost of living and how you can hardly even make rent on 30k.
The third factor, which kind of feeds off the second one, is that when you're 18 you think your ideas are going to change the world, and it's very, very hard to understand that every other 18 year old has similar ideas and most people burn out of the "big idea phase" several short years later. One of my friends wanted to singlehandedly make the next Halo style game when he was 18. One of them wanted to be the next Bill Gates. Two of my friends literally wanted to be Iron Man (autonomous flying suit and all). I wanted to be a socialist revolutionary and also film director (I switched to IT in my junior year of college). Bottom line is, people think they're always going to have the passion and drive they have when they're 18 years old, and by the time they're around 25-27 they're so burned out that they just want to do something mind numbing that pays the bills.