It used to be that way, with high diversity of opinions between subreddits.
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.
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.