Shower/Tub using floor drain?

[Darrin Alcorn]

I know there is an obvious answer to this since I never see it, but can someone tell me why you can't share a drain, whether a linear shower drain or a traditional circular floor drain, for a tub and shower?

I am thinking specifically in the case where you want to build a "wet room" where everything is waterproofed and sloped to a drain.