That’s because that’s all he has. From what I’ve seen and heard, he doesn’t even really understand economics all that well, and even still it doesn’t even matter because there’s no way he could try to claim it was all his ideas anyway, so it would be useless to him. He’s nothing but a pretentious narcissist who claims he thinks IP is not valid, but nonetheless maintains his copyright monopolies and wants to pretend all the moral foundation crap he peddles is completely original (even though it’s not). (And I’m not the only one who says so.)
He has to stick to moral arguments (and then try to maintain them through logical reasoning, as, of course he can’t be appealing to some supernatural being) because he can’t really make an economic argument. And it’s quite possible he can’t do that because he has no interest (and therefore no knowledge) of economics because he has a need to take credit as the originator of everything he says like some kind of balding Canadian Ayn Rand.