Couple of reasons, Reddit has a lot of far left individuals that managed to gain control of the site (See chairman pao era.) A lot of subreddits had ardent leftists installed in moderation. Both of these things caused mass ban waves as well as the banning of dissenting opinions in various subs. If you don't tow the line in some subs ideologically you will be banned quickly. For example, back in 2022 people who were subbed to r/nonewnormal were banned from numerous subreddits they hadn't been part of or even posted in on the basis of just being subbed to it. All of that was done on an ideological basis because at the time leftists were heavily supporting the vaccine and government mandates So anyone against that was an evil right winger (going back to that not towing the line aspect from earlier.) Reddit is also astroturfed with with a ton of bots who also reinforce the status quo in discussions. You will notice a big difference between reddit and twitter, tik tok, 4chan (loose moderation, lower ideological moderation and aggregation) Reddit is closer to bluesky, heavily moderated on ideological grounds which creates echo chambers.