My friends and I approached a well-known Gadol for a bracha when we were at a Shabbaton that included a singles’ component. He asked us why we weren’t at the singles’ melave malka taking place right then.
He told us that he was at a chasuna and he had 20 girls lining up one side of the mechitza for brachos and 20 boys lining up on the other for brachos. He said, “Why are you talking to me? You should be talking to each other.”
I also know of at least one Gadol who gave us his haskama to a singles’ Shabbaton.
My assumption (although I could be wrong) was that they were referring to singles over a certain age. In the first example, I think we were all in our 30’s at the time (there was one girl whose age I’m not sure of, but if she wasn’t in her 30’s, I think she was close).
For one thing, a 20 year old hasn’t really given the standard shidduch system a shot, whereas the girl in her 30’s obviously has and may need something different. For another, a girl in her 30’s is (hopefully) on a completely different maturity level, and as I wrote before, there is a big difference (most of the time) between a 20 year old talking to a boy and a 30 year old talking to a boy.