Shepard doesn't control the Reapers in the COntrol ending either.
Shepard is that charred lump of meat by the control rods. The AI that's controlling the Reapers is a construct made with Shepard's memories.

Well picture it this way, imagine playing as a Turian, watching the Turian grow up from birth, learning about their cities and culture.
What games let you do that with
any race? Mass Effect certainly never did that with humans.
That's way better than just working with them. I'm not really interested in playing as a human in the ME universe right now. I'm a human myself, I do human **** everyday. Let me experience something new! 
So play something else? It's too late in the development process now to add other races and multiple races would be a huge endeavor even if they developed a game around that choice from the start.