Waiting till E3, I guess. They want to splurge a bunch of trailers and release dates on us and then start releasing first party content through to the end of the year. Wario in June after E3, then Pikmin, then Wii Fit, and on to the holidays.
Because the game was probably originally planned as a Wii game and then switched to Wii U, so they didn't bother to put significant effort into the graphics. It would be ridiculous if the game only got out in Europe in August though.