What do people mean by 'fives' and 'tens' when dating

I've never really understood this whole "ranking" thing when it comes to attractiveness—like when people call someone a "ten" or say someone is "out of their league." To me, it just seems kind of dehumanizing to reduce a person to a number.

I get that the idea is supposed to be that more conventionally attractive people get a higher "ranking," but the whole concept of "leagues" feels self-defeating. Are people really avoiding talking to others just because they think that person is too attractive for them? That seems like such a strange mental block to have.

I guess I just don't understand why people frame attraction this way. Can anyone explain where this idea comes from and why people take it so seriously?