Reducing human reasoning to a few major questions, we can say that (1) finances, (2) complexity of choices, and (3) dendritic learning are three major impediments to a normal 4-year succession of organized pedagogical progress once college is “begun.” First, since education is becoming more and more expensive, anyone on scholarship who does not excel in his/her studies may lose their financial aid, thereby preventing their continuation; secondly, other-world opportunities, such as travel opportunities, family business, romantic connections, etc. get in the way of one’s initial “path” of an education. Thirdly, exposure to a formal higher education opens up the consciousness to brand new possibilities, and the change of declared majors often requires new starts, even different universities. There are other reasons – health issues, boredom, loss of interest, abrasive teacher-student relationships, feelings of inadequacy, etc. that interrupt the “well-made plans of mice and men.” Mainly, it is difficult to make and keep any four-year plan in this dynamic, volatile sociological environment.
I think there are two primary reasons one could point to in order to explain why drop out rates at universities are so high.
1) School is becoming unaffordable. Costs of colleges have been rising and there are so many stories about graduates being swallowed up and unable to pay student debt. It's not just the cost of tuition either, but textbooks are very expensive and trying to find housing near campus could be quite pricey as well. Even with financial aid, trying to pay for everything that comes with attending college could become just too much.
2) College doesn't suit everyone. In today's job market, it's almost a necessity to attend a university in order to have a degree and specialize in some field. As a result, most people feel obligated to attend college in order to increase their job prospects. Once people get to college though, they might find that it's too challenging and college just isn't for them, causing them to drop out.