We used to have social structures which provided guidance on how to find a long-term or permanent mate. Many of the young are left without that guidance and are going from the stereotyped gamer-in-the-basement to suddenly having to make up their own processes on the fly. Some of these will be very successful, but most will not.
In times when there was much more pressure to marry before having sex, a "10" guy would not bother with a "7" girl, and the "7" girl (not getting false signals) would be more likely to accept a "7" guy.