I think moderation on Reddit had the effect of cleaning out centrists as well, since it was a comment that got you banned from reddit and not your political position (e.g. a post which was positive towards a trump policy would get you caught up in the post-2016 moderation sweep).
You can see the effect on Indians. Quora was popular with Indians because it was intellectual and centrist in the western political spectrum, from a culture that has the right-wing as being Hindu-leaning and the left-wing as being Muslim-leaning. Indians are absent from Reddit comparatively.