Machaon said:
If it ain't broke, don't fix it.
They have pretty well thought-out ergonomics and their consistency allows us to migrate between bodies with little effort.
Any radical change would likely be a step, fall or plummet backwards. Why do change things for the sake of a gimmick unless there was some huge gain to be had?
If it ain't broke, don't fix it was probably Microsofts philosphy and it allowed Apple to flourish. Now Apple have the same problem with it's user interface. It's hard to improve it without a radical change whereas Android probably has alot more scope to change gradually.
This is evolution I suppose. The dinosaurs were pretty happy they way things were at some point but the small furry animals adapted and modified to the changing world.
Usually we don't spot extinction coming until it's too late.
