Some thoughts. First, I think that on the whole over the past 20-30 years we have encouraged young women to go to college more than we have young men. In areas where women are in the minority we see groups specifically designed to to encourage women in specific fields (the Society of Women Engineers for example). I don’t see those types of organizations for men as much.
Second, I think men are choosing other careers rather than going to college. The aforementioned trades is one. Another is the military. Men are not as interested on the whole as women to consider liberal arts degrees as they are no longer considered a general pathway to employment like they were in the 60’s and 70’s. Many of these opportunities are available to women, however, on the whole they are not paths that interest many and they on not encouraged to take those paths.