[masklinn]

> it gains the attention of the general audience, who often view /r/all.

It's not that they view /r/all, it's that they have not customized their front page, so they get the default set of subreddits, which I believe is simply the subreddits with the most members.

[Sniffnoy]

I think it's the subreddits with the most members, except that mods can set their subreddits to not be on the default front page.