It doesn't (so it's a good thing no one is claiming it does).
My point is that it's a vapid argument to claim that America 'just is' a capitalist country, as if that's an a priori obvious and good thing. America has always used mixes of social organization that you could today call capitalism or socialism (though the terms would be anachronisms, having changed meaning in important ways lots of times). Historically, we've had socialized libraries, school, police, military, post office; private health care, factories, etc. What 'the Founders' believed the country should be for themselves is irrelevant to how we should govern ourselves today. If today we think more socialism can be helpful, it's stupid to argue that America is a 'capitalist' country and thus it must always be so. We are and always have been a country where we govern ourselves with some capitalism, some socialism, and some policies that don't fit either model.
Socialism isn't the enemy any more than capitalism is the enemy. They're ways of organizing things, both of which we use all the time, both of which are sliding scales rather than binary options, both of which can be poorly implemented to disastrous consequences.