I think one of the main reasons for decline in content quality has to do a lot with the recommend feature. I'll be the first to admit that my effort I put into posting is considerably lower than it was before the recommend feature being added and that the quality of most of my posts has greatly diminished, because the recommend feature is so much more rewarding towards snide jabs at other posters (of ideologies opposite towards your own, of course) and one-off quips than substantive analysis.
As for the analysis of polls, I think that has to do with the growing distrust of polls across both sides. It's easier to dismiss polls people don't like as junk when you have the discrepancy between state polling in 2016 and 2018 to look towards. Quality pollsters like PPP have started working more on a private commission basis, and for whatever reason the public polls they release tend to be more D friendly from what I've noticed. It just feels like there's less high quality polls than there used to be. And of course with that said, that invites more accusations of junk polls, especially if one result is so wildly off base from what the rest of the polls were saying (not that outlier polls are necessarily junk).
