Why always (afaict) bulldogs? I’m thinking maybe their lower center of gravity helps. Do the dogs actually steer and consciously go where they want?
Because they look especially cute on skateboards?
Some (like Jumpy, who is not a bulldog) can.
I met in person the dog that I think was the first of them, and he was a bulldog. That might have prompted imitators, and bulldog-owners might have been more prone to train their dogs to imitate him.
For what it’s worth, when he found himself going in a different direction than he wanted, he would dismount, get back on the other way, and go in the opposite direction.
Our neighbor’s dog can ride a skateboard and even had a short clip of it shown on America’s Funniest Home Videos about three years ago. Half Jack Russel terrier, half beagle. She’s smart as a whip too. I often think of her as Snoopy’s granddaughter. (The dog, not the neighbor.) Doesn’t steer though.