AZ: There is not a doubt that the boys in the Litvish communities have more offers and options than girls. That alone makes it easier for them to pick and choose.
However, are you aware that in the Chasidishe oilam it is just the opposite? It is harder for the boys to find than for the girls! Just ask any Chasidishe friend regarding this. That is because the boys and girls do not have age gaps. They both marry at 18 so the population issues are not a factor. They also have a completely different process when it comes to making shidduchim for their children. The factors are the boys learning, the support, etc. I might not be giving the full picture as to the whys, but the fact is that the girls in the Chasidishe community have the upper hand in shidduchim.
Cherrbim: If you could hear some of the ridiculous reasons to turn down a reasonable offer, you could cry! For instance, parents have said “no” to a girl, just based on the fact that she went to a certain high school. Her family, her middos, her intelligence, her beauty, her sincerity = 0. Just because she went to one BY instead of another!
Yes, some of them are desperate, and some of the parents are desperate, but still unwilling to be open to going out with someone who is reasonable but not perfect.
I am not negating the age gap idea, but I am saying it is not the only reason. Again, it is multi-dimensional.