Communism doesn't require people to not be selfish or motivated by goodies, it just requires workers to own the shit they need to work, so they can't be exploited and coerced into socialized work for privatized profits. But regardless, capitalism is a system that rewards greed at every step of the way, which also isn't natural or neutral. There's a reason the people at the very top tend to be comically evil, they're those that the system selects for.