Reddit is not a community, it's a collection of communities. Each may be an echo chamber, but it's an echo chamber in its own way.
These days, all the default subs are left leaning, most are far-left leaning, which means most users have a partisan experience. This then impacts the overall makeup of the site’s userbase which cascades this bias through every other subreddit.
Sure, there are a small number of relatively low traffic communities that have held out, but they are now an insignificant proportion of the content on the site.
It’s a natural artefact of the voting systems it uses for recommending content. These tend to result in echo chambers because political extremism results in more engagement, and thus more extreme users vote more and have a larger influence on what is shown.
This is then amplified by the echo chamber effect, which distills the user base into ever more extreme positions as the moderate users find their opinions outside the evolving fringe of acceptable opinion.
The reason I class it as far-left now, even though I wouldn’t in the past, is two things:
Firstly, it is now plagued with extremist content, including calls to violence, which are tolerated by users and moderates alike.
Secondly, the opinions expressed have a left bias relative to other members of the left. There are plenty of moderate democrats, including people like Obama, who would quickly find themselves banned from many default subreddits for their more moderate tolerant opinions.
Banning users with moderate opinions is not normal in everyday life, but is routine in many subreddits. Including users sharing opinions held by moderate democrats.