I'm one of them! I didn't even know about r/selfhosted when I was on Reddit but I found this place when I joined kbin. I've been thinking on-and-off over the last year about self hosting so subscribed. I still occasionally look at Reddit in view-only mode though (largely for legacy content) so I also subscribed to r/selfhosted over there too last time I checked it.

It's not subscriber numbers that matter though, it's active users and quality new posts - people who go to the sub regularly, upvote, comment, and create content that causes other people in turn to look at the sub. I'm still a subscriber to a tonne of Reddit subs that I used to post and comment regularly on, and now don't. If every active Reddit user became a passive user then Reddit would grind to a halt overnight, regardless of how many users they notionally have.