Bob Fosse did NOT want to cast Grey as the MC, but the producers (I believe) told Fosse that CABARET came with Joel Grey, it wasn't a choice.
Grey really did the role to perfection. And he has great chemistry with Liza in the scenes they share.
"Some people can thrive and bloom living life in a living room, that's perfect for some people of one hundred and five. But I at least gotta try, when I think of all the sights that I gotta see, all the places I gotta play, all the things that I gotta be at"