They don't really ignore it. They experiment with it, and will continue to do so, until it solidifies its place as the industry leader in each genre individually.
"What are you talking about? It has already solidified its place!" -- I can hear the Wii well-wishers screaming already. No, it hasn't, at least not in all genres, but it's well on its way.
Consider the following estimates:
Consider the FPS genre (as an example).
Lets say that the FPS genre "appeals" (meaning they will definately buy the product, if its acclaimed and marketed on par with traditional good selling FPS games, barring unforeseen circumstances) to about 8% of all console owners, traditionally. Now, lets say (again as an example), that market studies have shown that the FPS genre actually only "appeals" (same definition as above) to 1% of the "special" Wii demographic (which has an exceptionally wide scatter). I'm not going overboard here with these numbers. Take a look at some of the (admittedly few) crossplatform Wii/PS360 shooters here on VGChartz for reference.
Wii, 50% marketshare, but demographic scatter makes only:
0.5% (~0.01 * 0.5) of all gamers (combined total market) interested in said game.
X360, 30% marketshare, but demographics make:
4.5% (~0.15 * 0.3) of all gamers interested.
PS3, 20% marketshare, demographics make:
2.6% (~0.13 * 0.2) of all gamers interested. (yes, X360 owners are slightly more interested than PS3 owners in shooters)
The FPS genre is one of the genres that is the most separated from the Wii demographic pattern. The Pro Sports genre is also separated by a fair margin. The Casual Sports genre, on the other hand, matches the Wii demographics very well. FPS, RPGs, Pro Sports (pro golf, as a game, is "casual" -- its true from the publishers point-of-view, don't hate me for stating it), Racing Sims, Flight Sims, Action Adventure are very clearly all in the PS360 demographic pattern. Casual Sports (incl. casual racing and pro golf), Party games, Platformers, Edutainment all fit very nicely with the Wii. Puzzle games, Music, and a few others are seemingly fairly balanced.
Lets use the FPS genre again as an example. Genres vary widely in development costs, but I think its fair to leave it to the reader to surmise what those costs might be, given a game in question. I'm just giving rough estimates here, since it varies too much to do a truly thorough analysis in a brief article. These estimates are not taken from any particular FPS projects -- they are merely here to provoke thought. Consider also that sequel projects usually cost around half as much as the original project to develop, and half again as much to port as well (ports benefit hugely from sequels, from the financial perspective).
low: 5 million, high 10 million
low: 10 million, high 20 million
low: 12 million, high 25 million
low: 15 million, high 30 million
low: 18 million, high 35 million (yup, it costs more to port to the Wii from the PS360, than it does from PS3 to 360 or vice-versa)
Lets use the high costs as our basis for comparison, since its big budget titles that people usually complain about the most.
Wii exclusive: costs ~10 million, nets 0.5% of Wii (0.5x multiplier) populace as buyers, at 50 "profit points" per unit. Normalized "profit points": 12.5, at a cost of 10 million (crossplat). 1.25 profit points/1M cost.
X360 exclusive: costs ~20 million, nets 15% of X360 populace (0.3x multiplier) as buyers, at 60 profit points per unit. Normalized profit points: 270, at a cost of 20 million. 13.5 profit points/1M cost.
PS3 exclusive: costs ~25 million, nets 13% of PS3 populace (0.2x multiplier) as buyers, at 60 profit points per unit. Normalized profit points: 156, at a cost of 25 million. 6.24 profit points/1M cost.
PS360 crossplat: costs ~30 million, nets 14% of PS360 populace (0.5x multiplier) as buyers, at 60 profit points per unit. Normalized profit points: 420, at a cost of 30 million. 14.0 profit points/1M cost.
PS360Wii crossplat: costs ~35 million, nets 8% of gamer populace (1.0 multiplier) as buyers, at "almost" 60 profit points per unit. Normalized profit points: almost 480, at a cost of 35 million. almost 13.7 profit points/1M cost.
Marketing costs are not factored in here, but, presumably marketing a game to its "crowd" will cost about the same for a Wii game as a PS360 game. This would actually make the overall cost of a Wii exclusive closer to that of a PS3 or 360 exclusive, or PS360 crossplat, so that's not a good thing for the Wii.
If you shuffle these statistics around (I'm not going to do it here), it seems as though the Wii would need more than 60% marketshare to justify cross-platform FPS games with the PS360, and closer to 70% to justify 3rd party FPS exclusives!
In truth, it actually costs more to do a Wii crossplat version from the X360 than it does to do a PS3 crossplat, and the same is true if you start from the PS3 (although the X360 crossplat, from the PS3, is definately the cheapest, in my experience, and this is probably why EA switched to the PS3 as the lead platform for their PS360 development -- it raises the "profit/cost" above).
From this perspective, its not in the best interests of 3rd parties to spend resources on Wii FPS games at all, and cross platform titles won't be worth it until the Wii gains even more marketshare than it currently has. ...for the FPS genre. Other genres are different, and 3rd parties will spend on the Wii when the marketshare justifies it as well.
In the end, developers are not "lazy" when it comes to the Wii. 3rd party publishers just won't spend dev money on it until those costs are justified by marketshare and demographics. Keep in mind that demographics changes with itself -- as the ball begins rolling in a particular direction, pretty soon there's a landslide. All the Wii really needs, in order to capture some genres, like FPS, is to get it marketshare close to 60%, and be demonstrating that is has momentum to carry it to 65-70%, in relatively short order (less than 6 months, or most of a FPS title's profitable shelflife).
Thoughts? Comments? Am I nuts? Even if my numbers are marginally off, do you think the idea essentially correct?