The wiki is very much the red headed step child of the HLP community. Sure, we all know its important, but editing the wiki isn't fun, creative or prestigious, so it largely gets ignored, or, perhaps more accurately, simply gets assigned a lower priority by the people who would be best suited to keep it up to date.
I've tried, unsuccessfully, to get people enthused about specific projects, but they typically go nowhere. There are a few small projects ongoing (like the User-made Weapons page, that I was supposed to work on last break, before personal issues ate up the majority of my time), but for the most part, I think people see adding things to the wiki to be the job of asset creators, while, for the most part, asset creators can generally find other things to do with their time than fiddling around with the wiki.
As a very rough estimate, the wiki probably needs between fifty and a hundred man hours to get it right back to to scratch and current - possibly significantly more if you include the effort of finding all the various mod and things that should be up there. That would be fine if we had fifty to one hundred active editors, but we don't, so its just going to have to wait until one of the very small number of active people find themselves with enough free time and inclination to start to chip away at that boulder.
Feel free to become one of those people, by the way - the time taken to post this topic could have just as easily have been spent on improving the wiki.