So the peak was in 2007. I think I know why.
In 2006-2007, there was an organized push on Wikipedia by pro-Israel editors to make Israel-related articles favorable to Israel. This provoked some major controversies, especially because at least one of the pro-Israel editors was a Wikipedia admin and abused their authority. (Eventually, they were "desysopped" for that, but it took years.) For a sense of this, see [1], including all the archived talk pages.
Wikipedia dealt with the problem by strictly applying the "reliable sources" rule. It became the practice that every single fact in Israel-related articles must be cited to a reliable source and properly footnoted. Anything that wasn't was deleted as "uncited" or "synthesis" by one side or the other. Until that time, articles often had text which wasn't cited to a specific source. The tough citation requirements anchored the dispute to factual information, and, though the process was painful, worked. The controversies settled down and the edit warring slowed to a crawl.
Those strict standards gradually spread to the rest of Wikipedia. Now, everything had to be footnoted like a doctoral thesis. Few people outside of academia write that way. This results in a big hammer coming down on someone new wanting to write an article about their new favorite DJ. Does he have mainstream press coverage that isn't from a press release, and did you cite it? If not, he's out of here.
Until you learn to write in that strict style, you can't contribute much to Wikipedia. For people used to blithering on blogs, Facebook, and Twitter, this is hard. That's what's discouraging new editors.
Writing for Wikipedia is now like contributing to a major open source project like the Linux kernel. There's a big body of code, and your changes have to fit in well and be justified. That's necessary. Wikipedia faces a constant incoming stream of PR, vandalism, and general crap. (Check out the ever-changing list of recent changes.[2]) The petty vandalism is mostly reverted by AIs now; ClueBot, driven by an ANN and trained on known vandalism, is quite good. The other problems take human attention, by volunteers tired of seeing similar annoyances over and over.
For the other extreme, of writing about anything with no quality control, see 4chan.
[1] https://en.wikipedia.org/wiki/Talk:Israeli_West_Bank_barrier
[2] https://en.wikipedia.org/wiki/Special:RecentChanges