Is there a specific reason why the "visit for x days" badges do not track across different communities? I kind of can understand the reasoning behind why privileges are tied to a single community, but why not this?
The entire system just isn't set up in a way for that to make sense. First, none of the other badges are that way, so these badges conform to the standard. Second, if you earned these badges by visiting different sites, which site(s) would the badge be earned on? Balance-wise, it shouldn't be all of them, but anything else is kinda arbitrary.