I’m talking about girls going for more than a bachelors. They’re going for a Ph.D. or a masters, and they put shidduchim on the ice so they can focus on the education. This causes them to age and by time they are ready to look for a shidduch it is so much tougher for them.
(It could be some of them aren’t even consciously making a decision to delay shidduchim, and they are in fact nominally looking for a shidduch while trying to become a doctor or lawyer or whatever. Nevertheless, that pursuit often takes their focus away and does delay their shidduch. When they finally are finished with their schooling, the quality men are married and even the raw numbers itself is insufficient if we accept the age gap problem.)
Another related point is that very often the highly educated girls think so highly of themselves that they feel all the men they are dating are beneath them, causing them to simply reject everyone.