1. When few people went to college, going to college was special: College back in the 1950's marked you as above the norm, hence college graduates historically have been the cream of the crop of society.
2. When everyone goes to college, college really loses its meaning and exclusivity. We all can't be Bank Presidents or CEOs. Most of us have to be Indians, not Chiefs. The idea that we can all be trained in college to run things is idiotic on its face. Huey Long tried to sell this idea - that "every man could be a king!" He was a crook.
3. Not all college degrees are equivalent. Most are bullshit. Degrees in Philosophy, Religion, Physics (undergraduate), Psychology (undergraduate), Pre-Law, Pre-Med, Business, Communications, Journalism, Sociology, Anthropology - and a whole host of others - are really worthless in the real world, in terms of training you for a job or providing real job experience. The reason is twofold: Some of these degrees are mere stepping-stones to a Master's program (the new College, since the old BA degrees are now worthless), others just are academic studies that have no corollary in the real world in terms of employment.
4. Not all educations are equivalent. In the UK, they have a grading system for college graduates. Almost everyone gradates, of course, but only a few take a "first" in their course of study. Most take a "second". If you just showed up and didn't make too much trouble, you got a "third" or "ordinary" degree. A friend of mine had one of these in Physics, and I didn't understand at the time why he didn't go into some technical career. I learned later that the only Physics he actually learned was how to stack pint glasses into a pyramid at the local pub. Degrees with low grade averages can be useless (although my GPA was a pathetic 2.5, due to the fact I flunked out of college).
5. While it may be statistically true that college graduates make more money, you are not a statistic: Statistics are backward-looking, so the data we see today is based on people who graduated from college in 1970. Yea, back then, going to college was a big deal - and you were someone special who would make more money. Today? Everyone goes - or can go - and college grads are just not in demand. Bear in mind that also college graduates are generally smarter than average, so it is no surprise that they would end up making more money - we should expect this. This does not mean, however, that their success was due to college. That would be confusing correlation with causation and no college grad worth their salt would ever do that, right?