Carry only champs in low elo?

When you're in low elo, what is the point of playing non-carry champions? I'm mainly talking about champions that have to rely on the team doing good. If you're low elo, you're relying on a bunch of low elo players doing good. Shouldn't every person on the team pick a carry and snowball champion? It seems the trade off is too much when you don't play a snowball carry champ.