As DY & always on thyme both point out, a bochur who wants to learn full time (as many do) has significant incentives to marry later, both to have less time that he may need to support (with no hope of a standard parnassah) AND to hold out for the possibility of “Life Support” from a rich Shver.
The “Kol Koreh” does not change that, or change any of the reasons behind it. I see this one being ignored, as it is not in the best interests of the bochrim (both materially & spiritually) on whom the onus is to change.