It is also, like many things in hardware, a software problem. The purpose of a keyboard is to interact with software. And that software is biased towards certain layouts. It is hard to change the layout too much without quickly becoming a niche product. Add to that the barrier to entry to making a hardware product is still quite high, and relatively costly.
For example, Matius was stopping one-handed keyboards for a while.
http://blog.monstuff.com/archives/000021.html
There were things like the Frogpad or the HandyKey Twiddler
https://www.youtube.com/watch?v=TmzYovAMHE4
https://www.youtube.com/watch?v=ciQVBNHrKKA