After working at it a while, they get good enough at it to get it in the basket. They see themselves improve and they like it. They see coaches as nurturing, where they might see teachers as judgmental. They see sports as exciting, because we tell them they're exciting. Even if they're no good they're nurtured, they're not judged, per se.
Sports are an entertainment, a diversion.
They're an extracurricular thing, perceived as fun. If you want children to play football, you don't show them other children in the backyard playing football. You don't give them plastic paramecium on the folding table in the basement of the middle school. You show them scientists and engineers from major companies all over the country, and you show them that these engineers aren't all old, bent, deranged looking white males with German accents out to blow up the world. That's a big deal, that's exciting stuff.