Why is the Daddy/son fetish a thing?

It seems so werid that I see a lot of posts and ads for people looking for an older man (50+) or a younger guy (< 30). Just thinking about having sex with a man as old as my own dad just makes my skin crawl. Now I know I have my share of werid kinks so normally I don't judge, I don't even judge you if told me you do this, but I want to know what the appeal behind it is?Sorry if this makes you upset, I swear I don't judge/ hate you if you do this.