I don't think there is a rationale; they just haven't updated the law recently. In their defence, they do also have things like Brexit to worry about. Apparent

I don't think there is a rationale; they just haven't updated the law recently. In their defence, they do also have things like Brexit to worry about. Apparently it is currently unclear even whether and where roller skates are legal, and it is occasionally claimed that wheeled bins are technically illegal on pavements, even though they are provided by local authorities and people are expected to put them in front of their houses on bin days. Of course, it's unlikely you'll be stopped by the police for using an electric scooter in a considerate way. But the lack of official approval is bound to prevent widespread use. Meanwhile, feral youths, without helmets, ride unlicensed, uninsured pit bikes across roads, pavements and other people's private land and the police have no resources to do anything about it. On the other hand, a middle-class middle-aged gentleman on a scooter would be much easier to catch, so do be a bit careful if you decide to defy the law. If you see the cops coming, run for it. They almost certainly won't shoot you.