Not a dumb question as there's only 5 people who actually know why this is.

When total war warhammer was released in late 2016, a new wiki became operational on gamepedia by mid 2017. by the time the two wikis were aware of each other, warhammer 2 had released and the gamepedia wiki had established itself as the most up-to-date warhammer wiki. back then fandom and gamepedia were separate websites who ran different versions of the mediawiki software and both wiki's admin teams were not comfortable using the other's interface, hence talks of a merger fell apart.

When fandom bought gamepedia 2019, both the wikis were part of the same website and eventually came to use the same mediawiki software, talks of merger recommenced. however we talked and decided to keep the two wikis separate as both had their distinct communities and wiki styles. instead, we started to collab and become sisterwikis, and we have been advertising and directing traffic both ways ever since.

As to why this wiki only has the 3 eponymous game pages and nothing else on warhammer is to protect authors of tw-warhammer wiki from plagiarism and to maintain our wiki's quality standards. so after a year of finding no editor willing to cover and maintain some 10,000 odd warhammer pages without plagiarising tw-warhammer wiki's content, we decided it's better to just direct traffic over there as they have a near complete coverage of the 3 games and all pages are actively maintained following every update, patch or hotfix.

So if you are looking for anything specific to total war warhammer, there is no better place than Total War: Warhammer Wiki

Total War: WARHAMMER Wiki@getfandom