Its because a lot of them have been sold the lie that it is possible, that these things aren't diametrically opposed and you can't judge a person based on specific traits.

This is all a lie of course, but its bigger than them just being stupid. The culture we live in is built to force that down your throat daily, and no one is immune to propaganda. And even worse, brainwashing never goes away completely even once you snap out of it.

The true contradictory belief all men hold is that you can hold women to principled standards AND not end up pretty terribly alone because of how few might ever reach them. None want to face the fact they might never find them and that makes them waver.