If people did not reproduce if they couldn't get a beautiful mate, then beauty would be widespread. But even if you can't get the most beautiful girl, most men still settle for what they can get, thus continuing the non-beautiful lines.

I don't know about beauty but I think in males there is a trade off like that between testosterone and the immune system.

I'd expect preferences to also adjust accordingly, so that there are always people on both sides of the distinction.