Man who preys both on the vegetable and animal species, is himself a prey to neither. He too possesses the reproductive principle far beyond the degree requisite for the bare continuance of his species. What becomes of the surplus of human life to which this principle is competent?

It is either, 1st. destroyed by infanticide, as among the Chinese and Lacedemonians; or 2d. it is stifled or starved, as among other nations whose population is commensurate to its food; or 3d. it is consumed by wars and endemic diseases; or 4th. it overflows, by emigration, to places where a surplus of food is attainable.

Trying to answer this would fill (and almost certainly has filled) numerous Ph.D dissertations.

There are a multitude of reasons. In no particular order:

* The utterly broken and ruinous US Senate, whose composition would be unconstitutional were it not written into the constitution[1], enabling a tiny minority of the country to block any meaningful federal progress on a host of issues

* The US's strong mythos of the Protestant Work Ethic, which leads many people to believe that people succeed or fall on hard times due to merit rather than luck

* Newt Gingrich, who in the 90s introduced hyperpartisanship to Congress, turning a body where members of different parties were friends and had good working relationships into a zero sum game

* The fact that one of the two major parties campaigns on "government doesn't work" and as soon as they're elected to their best to turn that sentiment into reality

* The impact of greed in the US and its successful capture of the media and significant chunks of regulatory apparatus

* The utilization of that media control to push divisive narratives that pit the lower classes against each other instead of focusing on the real problems and their causes

* The goldfish-like memory of too many US voters who buy into narratives like "they're all the same" or get frustrated when one party can't fix everything in 4 years and elect the other party - paying no heed to the fact that building is much slower than destruction or the obstructionist tactics.

That's just scratching the surface.

[1] Seriously, the Supreme Court has ruled it unconstitutional for any legislative body to be based on land instead of population. https://en.wikipedia.org/wiki/Reynolds_v._Sims