Or, not to be insulting to either man or beast, but maybe it was because he looked like an Bulldog.
Actually, he never had a Bulldog. He was a Poodle owner, two brown miniature Poodles, both called Rufus. They were treated like members of his family.
The Poodle ate in the dining room with the rest of the [Churchill] family. A cloth was laid for him on the Persian carpet beside the head of the household, and no one else ate until the butler had served Rufus's meal.
One evening at Chequers the film was Oliver Twist. Rufus, as usual, had the best seat in the house, on his master's lap. At the point when Bill Sikes was about to drown his dog to put the police off his track, Churchill covered Rufus's eyes with his hand. He said, 'Don't look now, dear. I'll tell you about it afterwards.' Source
Isn’t it nice to know that even historic world leaders can be as stupid about their dogs as the rest of us?