Why so much difficulty for people in college?

Here's a depressing article by "Professor X" in The Atlantic. The author is an intro English teacher at a community college who encounters large numbers of people who just can't do the necessary work:

The bursting of our collective bubble comes quickly. A few weeks into the semester, the students must start actually writing papers, and I must start grading them. Despite my enthusiasm, despite their thoughtful nods of agreement and what I have interpreted as moments of clarity, it turns out that in many cases it has all come to naught.

Remarkably few of my students can do well in these classes. Students routinely fail; some fail multiple times, and some will never pass, because they cannot write a coherent sentence.

Here's a response from Kevin Carey:

This is a common problem in education, both K-12 and higher, wherein we take the students with the greatest educational needs, give them the fewest resources and the worst education, and then call their failure inevitable. Here are some alternative suggestions:

How about not shunting the Ms. L's of the world into, in Prof. X's words, the "colleges of last resort" ? He talks of "the adjunct instructor, who by the nature of his job teaches the worst students." How about that not being the nature of his job? He says "the rooms in which we study have been used all day, and are filthy." How about cleaning them? How about not using adult education as a profit center, and instead investing that money in better adult education? Professor X says of his department chairpersons, "They don't mention all those students who have failed my courses, and I don't bring them up." How about mentioning them? How about bringing them up?

Via Matt Yglesias:

This [the fact that many people who go to college fail] is all true, but there are basically two ways of looking at the upshot. One would be to say that we have too many people starting college. Another would be to say that we need to do a better job of preparing more people for college. The growth in the wage premium associated with a college degree suggests the latter option to me. The fact that many European countries now have a higher proportion of people graduating from college also suggests the same to me. There's also the fact that currently at the college level we devote the most resources to the best prepared students while the worst-prepared students get the least resources (that's clear from Professor X's article) even though the objective level of need runs in the other direction.