Because a president cannot fire a congressman.
I don’t know about that but I do think there’s merit in finding a position for Romney (I advocate putting him in charge of restructuring the VA) because otherwise he’s apt to be sitting out in Utah where everyone thinks he’s next to God in terms of wisdom and all, stirring the pot, supporting who-knows-what kind of Mormon politicians, and shooting off his mouth. I think Romney has skills that can be useful, but just like Abe Lincoln did with Bates, Chase, and Seward, I’d rather have my rivals on my side rather than on their own.