Bear with me on this post; it's long but not angry (and hopefully is worthwhile...).
I agree that spin-offs generally are the result of laziness, semi-interest, and/or hesitancy on the part of developers and publishers. Wii has received "so many" spin-offs (or at least a handful of very disappointing ones like Soul Calibur, Castlevania, Resident Evil, etc.) because of this laziness, semi-interest, and hesitancy.
There seem to be a lot of developers and publishers that still prefer PS360 and would like to ignore the Wii's marketplace dominance, but I'd guess that their heads and share holders have become increasingly nervous and vocal as the economy has worsened and Nintendo's profits have risen (again). So, those at the top of these companies see the money over on the Wii side of things, but the actual developers and publishers' laziness, semi-interest, and/or hesitancy leads to such disappointing support.
But why do these people feel this way toward the Wii? My guess (possibly just taken form these boards and filtered / regurgitated) is that many game developers are stuck in a 20-year tradition. It's a tradition based in making games more complex and better looking through advanced and expensive new technology, and it has led to the creation and support of the 360 and PS3. Even their business structures may very well be set up around this tradition. Wii doesn't really follow this model, and while it has been number one for a little over two years, that's not much time compared to two decades of working (and growing up) under the now-traditional mindset in gaming.
Considering us posters are merely individual game consumers, we're not tied as closely to whatever business or development structures and mindsets have been in place for so long now. In other words, it's easier for us to acknowledge, adjust to, and embrace the Wii than many game companies. My guess is that it'll take more time than we think for the "majority" of developers and publishers to shift their mindsets to those of the Wii. (Except, that shift in mindsets might come about from older devs/pubs closing and new, "Wii friendly" ones taking their places.)
(P.S. This post is more general in focus. I have no idea how Extraction will turn out and I'm perfectly open to it being rad-tastic.)