I don't understand why paternity leave is even a thing, anywhere. Having children in the first world is an environmentally destructive hobby, as selfish as any

I don't understand why paternity leave is even a thing, anywhere. Having children in the first world is an environmentally destructive hobby, as selfish as any other. Sure, go for it, I don't mind - but why should we subsidize it? I'd love to spend 3-6 months with pay coding my dream videogame or climbing mountains, but the fact that I can't is not a societal problem. Why should child-rearing be any different?