The current “popular” reason why so little gets done in Congress is the wide polarization between the Democrats and Republicans, and that’s certainly a major factor, but I’d submit that there are other reasons that are just as important, if not more so.
The first is that the benefits of doing anything for the public good always take time to happen and often longer for people to recognize and appreciate them, while the negative impacts usually recognized and trumpeted widely and instantly by those affected. That’s why it took decades for legislation eliminating leaded gasoline and lead-based paint to be enacted. Lead in gasoline was a cheaper way of allowing gasoline refiners to market lower octane gasoline that worked in cars. Without using lead, refiners needed more highly refined and/or other more expensive additives. The same was true of lead paint. The benefits of “deleading” were spread across society, but benefitted the poor the most, while the costs were concentrated across a comparative handful of companies and industries, all of which had greater wealth and political power.
Dealing with environmental issues has run into the same difficulties.
Another problem is that some problems have no “good” solutions, because any financially and physically workable system will hurt many innocents. Yet the longer such problems persist without being addressed, the worse the problem becomes.
Immigration is one of those proems facing the United States. First, there’s no financial, military, and physically feasible way to halt all illegal immigration without becoming a police state along the lines of East Germany or North Korea. Walls don’t work, and deporting millions of border-crossers on a continuing basis becomes a huge financial and resource burden. Much of the problem lies in the fact that for many would-be immigrants, ANYTHING is better than remaining where they are, but to change those conditions in Central America and elsewhere would require essentially invading and rebuilding the socio-political structures in those lands, which would require resources and an effort that neither the regimes of those countries nor the American taxpayers would support. A “middle-ground” of allowing certain immigrants who would benefit the United States and absolutely rejecting the others would mean rejecting innocent people who merely want a chance at a better life. At the same time, failing to address the problem with clear-cut policies and laws will insure that the problem will worsen.
And the bottom line is that most politicians wish to avoid pain at a time when workable solutions will cause immediate pain for those with resources and votes.