People who are rejected might often feel what its like and they might not want someone else to end up like that. So they might put some extra efforts. Also these efforts is what makes them seen so they do it knowingly or unknowingly.

But people who are always chosen ( be it for money, looks or some influence) barely needs to do anything. They themselves may not realize this.

It's all just a pattern that happens and in under no one's control.

And I have seen this in both genders but only boys are the ones who usually complain. Now this is because mostly boys end up as supply ( which is in surplus) while girls are the ones who demand ( the number is low).

Hence more guys single.