AZ,
The boys are marrying girls that have a more realistic view of what they want. For simplicity let’s call the good boys (A) the ones that are going to learn 5+ years and the not good boys (B) the ones learning less than that. When a new class of girls start going out 90% of the girls want a type A boy. The problem is that only 75% of the boys are type A. The type B boys now have the pool of 10% of the girls and whatever percentage from older classes that have changed their view and will now settle for a type B. The problem is that there are many sub levels of type B, and the girl may only want type B-1 & B-2 but there may be more B-3 & B-4 boys out there which the girls is not willing to consider yet. Along with this, is the problem that to be a good girl all you have to do is say you want a type A boy and give off a good impression. To be a good boy, you have a laundry list of things that you have to do such as daven with a minyan and learn. Within that, there is how many times a week do you daven with a minyan, where do you daven, do you only wear a hat when you daven, what color shirt do you wear when you daven etc. and the same with learning, and if the guy leaves yeshiva to work because he looks towards the future and realizes it’s better for him to start at a certain point instead of waiting for tuition bills, it makes him a Tyoe C. The girls that realize early on that a type B-10 boy could be good also, usually don’t have a problem. Based on my experience (I married at the late age of 26 and my wife was 26 also) The girls looking for a tyope A usually start lowering their standards when the type B level they are looking for is almost depleted. As they say, the early bird catches the worm.