We recently outlawed them in my city. Didn't do anything. Everyone still uses them and no one enforces the ban. City next to us banned them years ago and I had no idea, same thing happened there. Continued use and no enforcement.
Enforcement is hard and expensive. I'd bet it's a question of weighing the cost-benefit of pouring resources into enforcement vs letting them peter-out and diminish over time.
Assuming a small city, it's hard to accomplish. But Toronto has the ability to influence major retailers. So it could be the start of the gas powered ones disappearing from shelves nationally.