One must wonder why

It's pretty simple actually. /r/politics got a reputation as a liberal echo chamber which shouted down conservative positions. In reality, that was never actually the case, and the sub was actually a place where spirited, primarily center-left discussions took place. Several years ago, I distinctly recall there being good debates between educated center-right and educated center-left posters. The only things which were ever reliably "shouted down" were fringe issues on each side - nobody entertained the merits of communism any more than they entertained the merits of climate change denial.

Then, after Obama's first election, the entire GOP took an alarming pivot to the far right when the Tea Party came into power, and you suddenly had mainstream politicians and pundits seriously entertaining very fringe issues. At the same time, many older individuals, who are more reliably conservative, and who were open to this new conservative narrative, started using the internet and social media in larger numbers. The result was a doubling down of conservative fringe "discussion" on this subreddit. Predictably, this was shouted down, as it had always been it's just that now, the fringe conservatives started to outnumber the moderate-right contributors, so what used to be earnest discussion with a side of lunacy, became vitriolic and unproductive far more often.

Anyway, the sub devolved into chaos and the general quality of discussion declined and the sub got a reputation as an echo chamber. However, in my observation it was not so much that conservative positions were increasingly rejected, but that the (previously rare) fringe ideas which has always been soundly rejected by moderates on both sides, started to become mainstream. In some way, this refusal to entertain fringe conservatism did make /r/politics an echo chamber, but it was honestly a pretty moderate one, if anything. Eventually though, most of the moderates on both sides abandoned the sub, and the only people who remained were the conservative fringe, and the liberals who mocked them - neither of whom were interested in actual discussion, even if it were possible.

What eventually happened, is that the mods here decided to take steps to force parity on the sub in order to correct it's reputation as a liberal echo chamber. To do this, they tried to select a new moderation team which was politically diverse, with the idea that it would bring balance to the subreddit. But that ship had already sailed, and the result was a team of sympathetic center-left mods who were concerned about the partisan reputation of the sub, combined with a faction of conservatives mods whose primary goal was to swing the sub to the right. What we ended up with was the same artificial parity we have in the mainstream media, where every position - no matter how fringe or patently ridiculous - must be treated as if it were earnest and worthy of consideration.

Then they implemented several new policies which, on the surface, were intended to calm the discussion, but which largely had the effect of protecting the newly empowered conservative fringe from earnest criticism. For example, they attempted to equate conservative tabloids like Drudge and Breitbart with left-leaning blogs like the Huffington Post and MotherJones by banning both in what must have been some very odd quid-pro-quo. It was pretty clear here that the conservative mod faction agreed to ban fringe sources which never had any chance at getting to the front page anyway, in exchange for some of the most prolific, popular and well respected liberal alt-news sites. Their decorum rules were put in place largely to insulate inane, idiotic posts from getting called out on being inane and idiotic. It no longer matters how much a post meets the dictionary definition of "ignorance" - you cannot call the post ignorant, or you will get banned. Of course, you can guess which side represents the majority of inane, idiotic posts which were suddenly protected from even rhetorically sound, and linguistically relevant criticism. Finally - and perhaps ironically - the mods decided that the average user base was not mature enough to handle political satire, so they banned it and pretended that the ban applied equally to conservative and liberal discourse. Which, I guess is technically true, provided that you ignore the fact that satire is a rhetorical tool which is historically favored by liberals - once again creating a de facto layer of insulation for the conservative fringe. Honestly, I believe that the conservative mod faction primarily wanted any reason to keep John Stewart off the front page, and like with the previous rules, the center-left mod faction was too concerned with erasing the alleged liberal reputation of the sub, that they didn't put up much of a fight.

tl;dr - misguided attempts at forced partisan parity were enacted where they were not needed, which predictably resulted in the same BS where we are supposed to entertain fringe liberal ideas as seriously as we entertain the moderate-left ideals which have always dominated the sub.