For the illegal electric mopeds/motorbikes I ask myself what stops someone driving an illegal petrol moped/motorbike around without type certification/registration/licensing/insurance? Why are electric vehicles somehow able to be sold bypassing those requirements?

For the legal "electrically assisted pedal cycles" as they are called in the UK, the solution has to be police actually doing their jobs: when they see the driver of a bike with a battery & cargo casually going >= 20 mph without any effort being put into the pedals (I spot these every single day, nearly all of which are operated by Deliveroo/Just Eat/Uber Eats): Stop them! Confiscate the vehicle! Prosecute the driver for driving an unregistered, non-certified vehicle, uninsured and without a driving license!