But more than just point out its commercial intent, I want to discuss a little about the topic of why Japan has washlets.
A washlet is a combination of a toilet and a bidet -- sometimes with other added features, but this is the core of it. Japan, specially overpopulated urban Japan, has a lack of living space. Given how cramped the apartments and houses in, for example, Tokyo can be, it makes sense to combine a toilet and a bidet to save space.
In Japan, it's sometimes cheaper to buy a $600 toilet + bidet combo than to pay for the extra space to install a separate bidet. Or sometimes the bathroom is so tiny that they have no other choice.
The US and Europe generally doesn't have this problem. That's why we're not all using washlets. Because we can just install a separate toilet and bidet for a cheaper price.
And if you want a heated seat, you can get a toilet with that for much cheaper than a $600 washlet.