The problem isn't the speed, there aren't speed restrictors on motorcycles or cars.
The problem is there's no safe lane for them to be ridden. There's no infrastructure accommodation for them. They can't be ridden on the sidewalk, and they're unsafe in regular traffic. Bicycle lanes aren't ubiquitous enough or designed well enough for bicycles, let alone these mixing with bicycles.
As usual, rather than raising taxes on the filthy rich to fund better infrastructure for the good of the people, they limit what we can do because it's cheaper and we have less power to resist, or at least, aren't organized well enough to exercise the power we have.