I'm skeptical that this is the primary reason. Everything you say is true but a LOT of people spend loads of money renovating bathrooms in the US. Just go down to a Home Depot and look at all the fancy sink, shower, jacuzzi, etc. hardware. Yet I've never seen a Japanese toilet in an American home. In general, toilets just don't seem to be something that gets any sort of special treatment in bathroom remodels. And none of the companies that make all the aforementioned hardware make anything other than standard sit toilets AFAIK.

I suspect it's just something that most Americans (and Europeans) simply haven't experienced or are even aware of. And it probably doesn't help that the initial reaction is probably negative--which may be why nobody's made a serious attempt to push these in the US.