Because it will not generate a high number of sales.Also, with Rayman both platforms already have a poor man's Mario.
Giana Sisters DS enjoyed good sales in Europe and I think made surprising jump in the US when it was offered at NewEgg for a good price. So it'll sell fine, though it might sell better within certain territories like Germany, Scandinavia and France rather than worldwide.
Anyway, this project needs to hit its goal, they really done a great job getting the gameplay to look unique and fun, and the soundtrack alone warrants a purchase.