1. The rise of deletionism.
2. The tendency for many pages to attract zealous guardians. I've had spelling errors immediately backed out. I expect that 99.9% of potential contributors quit at this point and never return.
3. Diminishing subjects to cover. All the "major" ones are done, all that's left are the billions of pieces of harmless trivia that deletionists decide, apparently at random, to do away with.
Note also that half the editors are under 22. This is probably why you can find vast articles on Pokemon and deletionists go around flushing articles on anything that happened before 1990.
Do you have any idea what you're talking about? Vast articles? No, the Pokemon articles were purged pretty early on; look at lists like http://en.wikipedia.org/wiki/List_of_Pok%C3%A9mon_characters or https://en.wikipedia.org/wiki/List_of_Pok%C3%A9mon_%28202%E2... which devote a few lines to main characters or major pokemon, and just compare some with their respective entries in Bulbapedia (where the Pokemon Wikipedia editors ultimately fled to escape the deletionists, much like the Star Wars editors earlier fled en masse to Wookieepedia).
Even the Pikachu article has been eviscerated: http://en.wikipedia.org/wiki/Pikachu (Hope you enjoy a list of awards and mentions... It's 'out of universe' material donchaknow)
Phew, what a useful compromise. Good work team. High fives all round.
At the very least complain about the species list if you want something ill-fitting for an encyclopedia.
Which is ... daft.
In WikiMedia's "Movement Strategic Plan Summary" they have an interesting graph to show.
http://strategy.wikimedia.org/wiki/Wikimedia_Movement_Strate...
So something must have happend around '07. What was it?