Quick clarification on scooters and back brakes: They do have them. The back brake is controlled by your left hand lever (normally your clutch level on a motorcycle).
From the few scooter riders I’ve spoken to, it takes virtually no effort to mentally swtich between braking on a scooter and a motorcycle. The overall dynamics are the same, and when you brake you normally pull in the clutch lever anyways.
And then there is the fact that Bicycles use a similar setup, but (usually) with the right lever activating rear brake and left lever activating front brake).