That kol koreh was not meant to convince guys to date younger; it was simply meant to make the promoters of the kol koreh feel good.
Think about it. If you want to convince guys to date younger, then you need to get the people who are advising them, to tell them that.
Who is advising bochurim when to start dating? Their roshei yeshiva. But most of the roshei yeshiva are not signed on the list. Yes, a few are, but mainly the list is trying to get the “gedolim”.
Well, when I make a big decision, I don’t poll the gedolim–I ask my rebbeim. They should have gotten all the roshei yeshiva of all the Lakewood feeders around the tri-state area to sign–since that is who the guys are asking. They probably did ask them, and they said no.