Well, yes, the calculus of the whole situation is slightly more complicated than comparing the two platforms as if everything else was equal. But if DotNW needed to both be a direct sequel to the most popular game in the franchise and be on the platform where the series supposedly has a big fanbase, just to barely cancel out that Vesperia was a better game (and let's be completely fair here: To somebody who hasn't been following either game closely, Vesperia doesn't immediately look like it had a mega-budget, and Dawn of the New World doesn't immediately look like a cheap cash-in; DotNW even comes out ahead in a few fairly important areas, like cutscene animation), that suggests that the fanbase really probably doesn't have a particularly strong platform-bias, eight years after Symphonia, on a completely different console generation.
I can see the argument for releasing the Wii version as well, and I'd prefer to see that happen, but the arguments against it (from it being a strictly inferior version of the game, to questions about whether people would really even care about it in the first place) aren't completely empty. It's not necessarily the stupidest move they could make.