Most American homes are not roughed in for a toilet like that. The waste pipe will be in the floor, about 12 to 14 inches from the wall. So installing one of these in an existing home is going to require changing both your water and waste plumbing and opening a pretty big hole in the floor and the wall to get at all of that. Additionally this is about 6x the price of a standard toilet. Not too surprising why they aren't that common.
They can be completely serviced from the button cutout - you can remove any parts through it (it was designed this way). I think almost all newer toilets in Europe are wall mounted. It looks better, it's very quiet (refill), saves space and works exactly the same... Here is an example video how to take it apart https://www.youtube.com/watch?v=es8SJ-1CFcU
It's serviceable, but it looks harder to access than a visible-tank toilet. At the 3m mark in the video, my hands are instinctively cramping just by looking at that tight space.
The difference is like working on a car in the 70s versus a Japanese compact car from the late 90s.
This and they are basically maintenance-free. I think most people don't know that these things are serviceable at all. They also often have two buttons that release a different amount of water. Good for the environment and saves you money.
I thought so too when these started to get common, but for one reason or another I _never_ had to fix one of these in like 15 years I've lived with them, compared to the almost regular maintenance the old stuff required.
I think the 'regular' style toilet tanks only require more frequent maintenance because they're inexpensive and people use crappy home store parts in them. You can buy five regular old toilets for the price of that wall-mount Toto.
My policy is to use high quality parts in the tank and I've found it pays dividends -- it's been years since I've had to do any maintenance on any of our toilets aside from cleaning.
I'm almost 40 and so far there has been only once in my life I had to do maintenance on a toilet, and I've always had "regular" ones. It was to replace a gasket.
My understanding it you go through the rectangle up top for most things. I've never done maintenance work on one, but they are practically ubiquitous in some parts of Europe. I would assume that if they required you to rip out the install to fix minor issue they would have been phased out.
https://www.homedepot.com/p/300820608