There are lots of boys in the “best” pool because they are put there by themselves, their parents or by virtue of the fact that they are in a “top flight” yeshiva.
There is a “crisis” because way more girls return from seminary on a high, looking to marry someone who will sit and learn for a long time. Realisticly, how many such guys who really can (not who say they want to) exist. The pool of girls wanting “x” is way bigger than the available pool of “x”. More girls looking for “x” get added to the mix year after year, but proportionately not as many “x men” get added to the mix leaving an imbalance.
Often overlooked is the rather large group of older guys who find themselves in a pool where there are not enough girls. Those fine bachurim who are honest enough with themselvs, and everyone else and are not saying “ill sit and learn for 10 years” because they cant. They are kovea ittim 2-3 or more hours every day, wonderful ballei middos but they are not “learners”.
They are the ones who usually end up marrying the 23+ girls who change their outlook from “learner” to a “ben torah”.