I suspect you'll find lots of stuff about culture, lack of information, parental support, weak schools, or no college guidance.
But what if it's something else, like--I don't know--the perceived ability to pay?
Take a look at this Census Bureau data. It shows changes in family income by quintile since 1967. On the top is dollars (current or nominal) and the bottom is percent change since the first year shown.
You'll see that the lowest 20% and the lowest 40% haven't seen much growth in income over that time, compared to the top 5%. (In case you don't know, 2012 dollars means everything is adjusted for inflation so you can compare a dollar today vs. a dollar at a time in the past. Nominal dollars are not adjusted for inflation, but a "dollar" in 1973 is worth more than a "dollar" in 2012 due to inflation.)
But this is a long view; since 1967 things have gotten better, for the most part, for every group. But try this: Set the filter to "2012 Dollars," then pull the filter slider to show a smaller window: For instance 1999 to 2012. You'll see that family incomes on the top chart appear to be fairly flat compared to the longer view; but on the bottom, which is more granular, you can see that income for all bands has actually gone down. This is an extraordinarily post-WWII run for America. And what's worse is that incomes have fallen faster for the lowest income families in the country.
What's happened to college tuition since then? Private college tuition has risen by about 20%; public universities by 40% in constant dollars. Federal aid has not kept pace; nor has state aid in most states.
So, maybe Occam's Razor, anyone?