CAR GOAT GOAT

The host does not choose a door at random, what he does is non-trivial:

The host is effectively combining what lies behind the two doors that were not chosen,
taking away a goat and offering what is left.

(So, if there was a car behind either of these two doors,
if you elect to swap, you will definitely get it.)

CG --> C
GC --> C
GG --> G