I think Mario having 2D platformers these days may actually be a factor as to why we barely get Wario Land games. Wario was there to fill a void that Mario was leaving when he ventured into 3D territories because, as you said, he wasn't doing any 2D jumping until NSMB came out.An interesting thing for me is how the Wario Land games were really coming out when Mario wasn't. He was first introduced in Super Mario Land 2 of course, and then the next game is the start of the Wario Land series, with the last game being Shake It! for the Wii in 2008 once the New Super Mario Bros series had already started. Even the prototype for a Virtual Boy Mario Land turned into another Wario Land. Maybe once Nintendo brought back Mario's 2D platformers after the absence they wanted to focus on him again and not Wario. Or maybe that does not make sense. I don't know.
I think it does actually. Despite them being developed by separate studios, it's still Nintendo that takes the decision whether to to make the game. They might not see the use in making a Wario Land title because they already have a 2D Mario series that's working great and that Wario may get overshadowed by it.Yeah, but this honestly might not make much sense if the Wario Land games are made by other studios anyways.