I'm not sure how much I disagree with you, and your reason is discrepancy in adoption of the add-on as compared to the original platform.
But I will disagree. 3rd parties supported Kinect pretty much just as much as they supported Wii as of 2010 onward. Why is that? It's because MS did a good job at pushing it. It comes back to what I said.
But whether this is all true or not, it doesn't change the fact that it can all be done on one same platform to a certain degree of success or not. The same could not be said for computer components on the 1st consoles of the time, which is what prompted the generations in the first place.
164 third party games with a gamerankings score above 60% released in 2010 for the Wii ...
28 third party games with a gamerankings score above 60% for Kinect IN TOTAL
It's not even close. The Wii which (based on many people's claims) has awful third party support for a console is receiving about 10 times the support of your successful add-on. Add-ons get abysmal support.