I tried to explain this to my normie friend years ago. He would try insanely hard for months on end back then and sometimes he would get lucky and get a girlfriend. But as online dating spread the time that each new girlfriend would spend with him was getting shorter and shorter.
As Tinder took over now he can't even get a girlfriend at all. But I am guessing there are high-tier normies who are in the shoes he was in 5 years ago, where if they try insanely hard they can get a girlfriend still.. but how long before she monkey branches.
Even Chads have this problem to an extent. It doesn't take long for women to get bored even for a Chad, and there is always tons of other Chads available. And when that girl leaves Chad for another Chad.. it means the first Chad is now on the dating market again.
Thats another reason why the traditional marriage is the only way. Has to be full marriage before sex, and once married there is no way out.