Which does no doubt have something to do with the end of WoT, but more generally it's an internet-wide shift, with the social media cannibalizing the older generation of communities and message boards. Of course, the people who have been here for a while already and have friends here wouldn't easily drop that entirely in favour of Facebook, but as Larry mentioned, they are growing older, getting jobs and families and so on, and have less time for this - that has always been the case, that's why a community needs the new blood to keep thriving, but when the new blood isn't coming, then this is what you get. And of course this kind of thing works in vicious circles, the fewer new posts there are, the less people will visit and make new posts of their own.
I don't think the politics discussions drive people off, as such - it's more the absence of other discussions that makes those not interested in politics lose interest. It's interesting that politics discussion seems more resilient to the dying off than other things - probably because Facebook and Twitter are hardly suitable for real debates on those topics, while they are very much suited for discussing personal news. That's perhaps also the reason why the Books and TV/Movies board have more activity than the Comm board, these days, not that that's saying much.