So what if most rich people are not Brad Pitt? Just pick one you prefer, whatever the criteria is based on what’s available. If some people are not Brad Pitt, and you have such a high standard, then just say no.
Basically legal status of marriage should be the same with legal status for prostitution.
Any reason to prohibit prostitution (it’s such a bad deal) can be applied to marriage. Any reason to believe that some people may want to get married can also be applied to prostitution.