Although RMRK has always been an RPG Maker-related message board, it wasn't always like that. The height of the forums' "activity" was at a time when the RM aspect of the community was least prevalent, actually. The general/miscellaneous forums were much more active a few years ago, and most community events had little, if anything, to do with RPG Maker or game creation at all. Nowadays, it seems as though the message boards' activity has certainly shifted back towards the RM boards, which in all honesty is a good thing, and explains why traffic has increased much more lately. And almost every community event in recent times that I can recall has been related to game creation in some form. This is a great thing, in my opinion; the life of the community doesn't rest so much in its regulars as it does in its RM users. After all, without the RPG Maker resources, we're just a meaningless kit.
As for my own activity, it has a lot to do with everything I just said, and how it pertains to me (or doesn't, rather). I don't use RPG Maker anymore. I occasionally pop it open when I'm feeling particularly inspired, but that doesn't last long, and I never really stick it out. Game creation is just a hobby I've had to put onto the back burner. As such, my only compulsion to return here are the friends I've met over the six and a half years I've been here, and even then, I see most of them in IRC anyway. And that brings me to my overarching point: If you're looking for activity, hang around the chat room. It's a truly separate entity from the message boards in that it has absolutely nothing to do with RPG Maker; we don't offer help or resources, and the only discussion about RPG Maker are the few people who happen to be using it at the time.
Whether or not you do, though, just remember that there's really nothing wrong with the site. Having been here for a majority of its lifetime, like most of the other regulars, we've seen activity rise and fall like an unpredictable tide. And nearly every active member who joined before me has already replied to this thread, so that in itself should be an indication not to fret over it.
And sorry this was so long.