This is a complex issue that I've been thinking on as a user and an academic that is interested in how we aggregate our content. I think its a bit silly to take this as a personal attack; rather, this is a result of a different curation approach by users, where subreddits are "pruned" rather than specifically added to a stream.

r/GlobalOffensive, Note how many game-related subreddits are on this "missing list", too ( r/Overwatch r/DotA2 ). This is, from what I can see, due to how these will have extremely active communities that can upvote stuff to the front page a lot, yet have a niche audience.

The end result is that posts like this one show up on r/all . This is not a bad post, or a mean-spirited post, its just a post that makes no sense to someone that doesn't follow LoL.

As a result, users who browse r/all a lot get annoyed by posts that they don't care about showing up and pushing down the stuff the do care about (exhibit A: super-bowl posts. r/superbowl posts are fine).

Since filtering was given to everyone, users have been taking advantage of it, and the end result is essentially a reverse-curation from the subscription system. Instead of building a front page with only the stuff they've clicked on, some redditors are choosing to start with everything and remove the stuff they don't want to see. The benefits of this include:

Exposure to previously-unknown subreddits

Far greater variety

Major breaking-news events from unsubscribed subreddits show up on a redditor's feed

I don't know if that's right, but that's what I, a lowly user, see. I support this idea, because it seems to adopt the "pruning" approach and generalize it for any visitor.