/r/popular isn't filtering with any bias to the left. The problem is that /r/the_donald has destroyed every other conservative or republican subreddit. Even /r/conspiracy has a forced policy against anything anti-45.

/r/conservative used to be a fair place for fiscal conservatives and social conservatives. Now, the rules are set up that criticizing 45 in any way or form is an bannable offense. Want to talk about how spending tens of millions a month just to transport 45 and all his family around is a complete waste of money? Ban.

So, the quality of the posts faded and therefore users who are sick of it have walked away and those subreddits have diminished in popularity. If you can have a discussion, why go to a place where someone is just going to unintelligibly scream at you?

Insular policies are to fault.