Many keyboards are dished. IBM did that with the Model F and M, with the idea that business typists (their market) were typing in proper clerical desks or a typing stand that held the board a few inches above the thighs. A lot of "proper typing" and key positioning has the implicit assumption that the user's forearms are free to move in all directions. The most common modern arrangement is "forearms on the table", which limits mobility, particularly between the bottom and top rows. Using the top row often requires bending the wrists back, wheres it is a simple finger motion on a low-positioned keyboard.
Keyboards don't need to be dished. Many modern keyboards aren't, and work just fine. Particularly laptops.
Frankly, I'd love to get a board that was curved up in the middle, so the top row would be *down*