Next was poor sales. Wario World sold poorly and basically killed the IP. This was then furthered by GoodFeel trying and failing with Shake It. Then, as mentioned by you, the original dev team, R&D1, split, so they couldn’t backpedal on them to make games.
Finally, you have WarioWare, which during the Wii/DS was outselling Land, with Wario’s highest grossing games being Ware for DS and Wii. Given the above circumstances, it made sense to push Wario down the direction of Ware. Land wasn’t going anywhere and lost favor. Mario could now fill Wario’s place.