Mainly because the Wii is a system. It's stationary. The chances of it being lost, stolen or broken by dropping, liquids or collisions is minimized. As well as the capabilites of the Wii surpasses the handhelds. The majority of people who obtain gaming systems is aimed toward age 10-17, which means that parents will be the ones purchasing them. A -parent- with things better things to spend money on like morgage, food, lights, and gas than spend money on a 300 dollar handheld that can be stolen by kids or lost by kids--namely when they've spent 400+ already on Wii's, PS3's, Xbox's, Psp's, and DS's. These things effect how well something--anything--will sell. It is very risky to put the game out on a system that is not out at all right now, cost as much as a used current system. It's safer to put out the sales on something that is out already. The Wii would have been the best choice. Second would have been the Xbox for America and Europe, or Second in Asian countries for the PS3. You have the convience to buy a game on a current system that has been paid for, for a series that hasn't been acknowledged widely by gamers outside of Megaman fans, this is a risky move.
It's not about faith, it's about having the sense to look at it logically. You can have all the faith that you can fly off a building. However, don't expect to fly. Will some sales be made? Yes. There are fans of the series that have more than enough money to cash out for this. Will it be how much they can make? No. The 3ds will sell. Without a doubt, but given the price and a series that's not talked about outside of fans? Not very well. Megaman ZX, will you take the stand?