A steady decrease... which, frankly, is rather normal for games of this age and the aforementioned reasons regarding the fact that this site and most others are built for a single platform while MC is dipping a rather large foot into other platforms.

I'm sure you'll find some form of an increase on other platforms.

Minecraft as a whole has been a slowly dying game in general. Many major youtube personalities like Sky Does Minecraft have quit from Minecraft, the main creator notch didn't even wanna keep the game under his arm due to the amount of stress it gives. I think though with Microsofts increase in improving the game and the competition between Minecraft and Roblox that it will slowly grow again, no matter how brief.

Yes, not because of anything this site has control over however. Not only is Minecraft becoming less and less relevant with all Minecraft related media experiencing this, but it's userbase is becoming younger, and it is becoming less a PC game and more a multi-platform game where PMC and most Minecraft fansites are geared primarily towards PC play. That being said, PMC is still the second largest Minecraft fansite after Minecraft Forums, and the gap seems to have shrunk (which honestly surprised me) and I don't see another site coming close to PMC and MCF in the forseeable future.

I'd say that activity is slowly decreasing but I feel like pc minecraft isn't getting any more popular either, as far as I'm aware pmc is still one of the biggest minecraft community websites.