This could be because of the different teams handling a Wario game each time.But Wario doesn't have 1 single style he can call his own, that's what I like about the series, each game is unique. Maybe they're out of ideas? Dunno, but it really seems like Wario's always at the end of the joke stick. He was kinda created as a joke but if so, well, we love this joke, that's for sure... NINTENDOOOOOO!!!!
This could be because of the different teams handling a Wario game each time.
Wario World = Treasure
Master of Disguise = Suzaku
Shake It = Good-Feel
The original team behind Wario Land 1~4 has moved onto WarioWare from that point (All WW games after the first were jointly made with IS)
Needless to say, even Wario's "home team" doesn't have a firm enough grasp on him.
Actually data that we are aware of heavily suggests that Land is the better selling series, Land's problem is the lack of a consistent delopment team, after R&D1 dissolved, where as Ware was lucky to be in the hands of SPD1.From what i heard Wario Ware have usually more sells than Wario Land so it makes sense that Nintendo supports it more than Land.