This is part of the problem. The community "moves" but the old wiki isn't down, and it picks up contributors from sheer SEO rank.
UESP predates Fandom and was extremely fleshed out, and is frankly superior to the Fandom version at every point in history. But even with the "head start," UESP has really suffered due to the existence of Fandom, for no reason other than artificial SEO dominance.