Well, as far as I can see its like this.It is about weight and the porkers they keep producing is one of the main reasons they are firmly locked in 4th place for sales. Mountain sleds are supposed to be light and agile. Getting stuck and having to lift them out of a hole, riding aggressively, and being able to float over the snow all require light weight. The Sidewinder MT-X is just a lake racer hyper sled with a long track. It breaks no new ground and will only appeal to a very small segment of the market which has already been served with the 1100T and the turbo'd Vipers.
Yamaha Corporate, (and I suppose everyone who owns stock in that company), rather obviously DISAGREES with your revelatory insight. As does every person who has recently bought a new Yamaha and all the guys that are ordering new Turbo Sidewinders right now.
There is more to mountain snowmobiling that just having the lightest, most fragile, easily broken, shortest engine life sled money can buy.
For me, I rather like the idea of a bone stock full warranty factory boosted 204HP Turbo Sindewinder.
In your world its not possible to take out a Nytro or a Viper and have a good time. In mine, I have been doing it for 7 seasons now and LOVING it. And will no doubt be riding Yamaha next season again.