I used to wonder this myself until I switched High Schools my Jr. year, we moved and there was a reshaping of the school districts. So instead of the typical Upper Middle Class public/private schools I'd been attending my whole life, I went to a school that was about 80% blue collar. A lot of these kids (white) didn't go to college either, (it's significant to note that poor whites and poor blacks attend college at about the same rate 56% & 57% respectively - according to a USA Today Article..I'll dig it up later.) They didn't go because for a lot of reasons:
#1. Their parents didn't go, so it placed a cultural barrier that it made it seem as if it wasn't a part of their reality and/or that it was only for rich people.
#2. Money, a lot of them were afraid of debt and weren't aware of the resources available to them. 80% of all students are on some financial aid, so people didn't realize that only the top 15% of wage earners or so, can really afford to pay for college out of pocket. Therefore, borrowing money and drumming up grants was an issue for the majority of students.
I had a friend ranked 4 in my class, he (and 7 others out of the top ten) never attended college, afraid of the cost....even though 4 years at the state school (which they could all get into) would only cost them about 12k for tuition....which is CHEAP as far as college goes......12k was one semester where I went to school.
#3. Not sure of how to start, to some of us.....sending out applications, taking the SATs and filling out financial aid forms is foreign to some people.
#4. It's esoteric, it's not really graspable, it's unfamiliar. It seems far off and not easily attainable. Think about it, no one in your family has gone to college, you know few people who have and you're school isn't focusing on it. You're not going to have as much impetus to go as someone like myself who see his parents degrees on the wall, hears about it, knows few adults who didn't go and has the fact the he's going pounded into them by his parents.
Basically, my parents didn't really give me (or my siblings) a choice of going or not. I could choose WHERE to go, but not if I was GOING to go. Just ask my Brother, who got smacked up side the head (twice) when he proclaimed to the family at dinner that he didn't think he wanted or needed to go.
In the end, it comes from your family and your environment and what the norms are. If going & graduation from college is the norm, you're almost sure to go....if it isn't you probably won't go and you may not finish.