Once upon a time Wario was quite relevant. I remember all the ads and promotion Nintendo gave to Wario. They actually treated it like it was important.
Somewhere along the way Nintendo stopped caring. Why? Why did they start neglecting Wario?
Intelligent Systems still does though, and they made WarioWare (and some of their staff were involved in Wario Land 4)...
Actually, that makes a lot of sense. Nintendo barely seem to ever promote anything by Intelligent Systems. Fire Emblem before Awakening got ignored, Rhythm Heaven gets very little advertising, Paper Mario sometimes seems like it may as well not exist for how much attention gives it compared to the platformers and kart games...
Most of its staff (including a fair chunk of the people involved in Wario Land 4) were folded in nintendo SPD #1, though.
Cult classics don't sell 1 million on most installments. I think it's really the perception of Wario as a Mario character that explains why people aren't proclaiming their love for the Wario series, or something.
I feel like it became a break-out success early on due to the "play as the villain!" marketing and the concept of an "evil" Mario that got most people interested. After games like Grand Theft Auto or choose-your-own alignment games came out, playing as the villain isn't really a big deal anymore. Not to mention nowadays he's not really even portrayed as a "villainous, evil Mario" anymore, just a crude, smelly, fat guy. Not that I don't love those facets of Wario's personality, but it's not who the average gamer wants to play as. You guys are blaming Nintendo for not promoting Wario anymore, but I think that they just realized it's not profitable for them to do so. Unfortunately, Wario isn't exactly what the market wants anymore.
I dont think people really see Wario as a serious character nowadays, hes kinda just become another Nintendo "b-character", like another of the characters they just use for party games and Mario Kart. I dont think the rest of the world even considers him to be any more than that nowadays.