I feel like at that number Reddit is in the goldilocks zone for being a useful social media platform -- big enough that there is tons of engagement, but small enough to not drown out anyone. If I want to, I can make a post about a hobby project on Reddit and (if it's actually something interesting) it'll get quite a bit of attention. If I post the same thing on twitter, it'll be lucky to get a tenth of the attention.

I do wonder how much of this is due to the lack of emphasis on a poster's "credentials" though. Reddit seems to be the last online platform where anyone can contribute to a discussion without being judged for how "popular" someone is.