Possibly because you're exaggerating. In 2012 the
gap was 56/44. So 1.27 women for every man. It probably doesn't get reported on very often since women have outnumbered men in terms of total enrollment since 1979. One explanation might be that there are many more professions that are male-dominated but that don't require a college degree. Skilled tradesman, for example. Construction. Anything where physical strength is a prerequisite. So if you're a man who doesn't seem cut out for college then you have options. If you're a woman then, perhaps, you have fewer options. So there's greater motivation to get a degree.
It might also be worth noting that the gender gap
decreases substantially among "traditionally aged" students (24 and under) as family income rises. So the gender imbalance is coming from poorer students and older students.