Their actions are deliberate.
Nintendo doesn't work well with third parties. Or not nearly as well as Sony/MS do. I think Sony/MS treat third parties better as a whole. The term wine and dine is probably most appropriate here. In my opinion, this is something Nintendo has never been overly great at even in pre-existing consoles. As for this current generation? I think a big selling point of MS/Sony right now is having this fully-fledged, robust online distribution service. It provides easy advertising space for them, easy distribution space, and a whole slew of other options.
You have a staff of talented developers and you ask them to work on hardware that is essentially 10-15 years old? How hard of a sell do you think that is? You don't think that people at the cutting edge of their industry want to work with cutting edge technology? I'm sure that just making fun games is a lot of motivation but don't think for a second that working with the latest technology and keeping up personally within the industry drives a lot of talented developers as well as well as challenging themselves with newer, greater technology.
We also have the factor that Third party games just don't seem to sell gangbusters on the Wii compared to the HD consoles. So what is the point in bringing games that will get average sales at best to what essentially amounts as the 2nd place console market? (HD vs Wii).
Additionally to the prior note, I can say that personally, I've 'never' bought a Nintendo console for a third party game. I would imagine that many others are similar to me. It always been Zelda, Mario, Metroid, Star Fox, etc first and other games second. This is important because Third Parties games always are dealing with a slew of Nintendo-fans who are Nintendo games fans first and everything else second. (A phenomenon you just don't see from Sony and really only with Halo from MS).
In short, Third Parties like Nintendo console sales but don't like third party software sales / typical or assumed userbase mindset / features available for them to use / Their staff of developers has more to gain by working on superior technology and as a result third parties are most likely pushing Nintendo to become more like the HD consoles (Atleast in certain ways).
