I guess they just don't want to be seen as competing with all the other wikis for specific franchises. Bulbapedia exists for Pokemon stuff, Mario Wiki for Mario stuff, Wookiepedia for Star Wars, Memory Alpha for Star Trek...
They want to be seen as a place for knowledge about a variety of topics, not one that's heavily focused on a single subject.
Wikipedia and the Pokémon wars predate these wikis. Note that many of these are hosted with Wikia (originally named Wikicities), which was Jimmy Wales's next venture after founding Wikipedia (he's moved on to The People's Operator). Wikicities was launched sometime 2005ish, but Pokémon articles and no-name garage bands were already a hot issue at the time.
thats a great point, look at the Karen page on bulbapedia: http://bulbapedia.bulbagarden.net/wiki/Karen,
there are lists of pokemons she uses on every game she appears, their movesets, quotes from her, artwork, appearences on the manga and trivia.
I personally lean toward inclusionism but I don't really think any of this information fits wikipedia.
They want to be seen as a place for knowledge about a variety of topics, not one that's heavily focused on a single subject.