Because among college men, the more senior you are, the higher status; also the single women of your age either date you or they date some guy younger(naah, women don't do that) or they date some guy outside of college(a bit harder) -- plus single women feel that it's "now or never" since it's the final year in college.

It USED to be be the same thing when you were in highschool before tinder and social media: as a male, the more senior the higher status you had -- i.e. 9th grader males will just drool at their female coleagues going out with more senior males, until in 12th grade you finally hit payday.

Not so anymore because tinder and social media allow females to reach a much broader male audience.

It's the same thing with women in their thirties -- they notice they get a lot less male attention -- first the bad boys stop noticing them and a couple of years later even the nicest of guys won't give them that sweet validating attention women crave, so the smart ones settle down with a nice guy in her early thirties, the not so smart ones end up basically cat ladies.