some of you mentioned earlier, but it’s worth mentioning again. Many believe it’s the age gap. Think about it logically, in chassidish circles, they don’t have as bad as a shidduch crisis as the litvish world does. And by them the boys get married around the same time as the girls. About 18. (someone did once mention, that if there is a problem in the chassidish world, he thinks its because everyone is so particular to get someone from their exact chassidus… and just 30 years ago, they did “intermarry.” BTW, there was a “shidduch crisis” in the satmar community, after WWII. They asked R’ Yoel what to do, and he said, to marry sefardim. (if you ever noticed there are some vert dark chassidim)
back to the litvish world, think about it, every year a whole new “grade” of girls get out of sem and are automatically on the shidduch market. However, the boys, there’s no such thing. A boy 3-4 grades older than her, decides than that he’s ready for marriage so he has : all the girls his age, and a full 3 grades bellow them. I actually know of 2 sisters, who are 2 years apart, one married a boy a year older than her. The younger one than got engaged to a boy from the same class. (3 years older than her)