My hobbyhorse theory on where things went wrong is more on the money side. Not that money and corruption in politics is new, but that nowadays most members of congress have to spend more hours working the phones pumping rich people for money than they do talking to colleagues or working in committee / on the floor / elsewhere.
Staff do a lot of the work, of course, but staff can only present arguments to the member - they don't get to vote themselves (also of course). We're in this political realm where the job is not just 'policy optional' but 'everything but voting optional' in terms of what congressional members used to do; some of that slack gets picked up but not in a way that's reliable.
Some members (on both sides of the aisle) are still fine, and still put in the work for actual policy development toward what they see as solutions to problems. But a lot of folks aren't there for the day to day work and don't really care about it that much.
I have other theories about how making so much of the congressional work publicly livestreamed has created more problems than it's solved, insofar as it works to penalize friendliness across lines, but that's less thought out and I'm not sure how I feel about its implications if true.