Is it easier to develop 6 different games with different mechanics, story, and moves? I’d think making the same game across all systems would be easier cheaper and better for everyone than developing essentially 6 different games with the same name. Aside from having to accommodate for differing controls (Wiimotes, Keyboards,etc.) should the games really be that different?

This answer is pretty late but different studios were in charge of making different versions. This optimizes the development for each specific console, rather than having to go back and tweaking each version from platform to platform.