Probably because no one has one. At least in Norway the best you can do is reserve one by handing over your name and address, no indication of delivery date, no configurator.
This isn't a computer. There is more to buying a car than a single spec.
Mercedes is a fantastic brand. The interior is premium and luxurious. You don't have to worry about service, support or the company going bankrupt. And it overall is a really well designed car.
There are a small number of people who will pay the Mercedes premium. There are a small number of people who will pay a premium to get electric. The intersection of the two is not a large market, IMO.
Reviews have been generally excellent so far.