as a person that came from the 3rd world country and new in fediverse environment, i genuinely would like to know about this.
edit: thanks for the replies! sorry, i literally don't know the reason since i'm not a western lol. twitter/x is too biased especially when musk openly supports trump so i came here and seeing fediverse is mostly are harris or biden (when he's still up for the candidate) supporters. don't know about reddit tho, i only use reddit as a forum for linux and programming stuff.
Reddit's early days were also far more left leaning then they eventually became.
When you have a small niche of nerds who enjoy discussing topics and ideas, then far right wing points will get downvoted to hell because they are, quite frankly, dumb, divorced from logic and the real world, and don't stand up to actual critical scrutiny.
Reddit got more right leaning as it grew and expanded into the general population and more dummies started upvoting dumb posts, then got more right leaning when right wing political orgs took notice and started trying to influence it, and now seems even more right leaning because they've changed their algorithms to prioritize controversial comments and posts that get people angry because it boosts engagement.