The authorities have been trying to control the ebike market for several years and previous attempts have not been successful. This time I believe it will be successful.
Almost daily I see police with a recovery/flatbed vehicle seizing unregistered machines. There seems to be a clear mandate to get the no longer legal ebikes off of the road.
Like @JanJal, I thing the main issues have been around safety. When I first came to China in 2004 ebikes were small, light, and only did about 20kph. I also believe they were only 12 v.
Now ebikes are bigger and heavier than a gas scooter, 72V and capable of over 60kph, and still no license, insurance, or training is required to ride one.
I have been hit by an ebike once, whilst riding my bicycle, and nearly been wiped out on at least two other occasions by kamikaze ebike riders.
I have seen several ebike crashes caused by riders who do not have proper control of their vehicle (using feet as brakes, slamming on the front bike causing a low-side and dropping the machine, panicking and just freezing as they plow into other vehicles), this is a training issue. Alternative, let the untrained ride smaller and slower machines.
The market needed controlling. Yes there will be some waste, but in the next 4 years some sanity will quickly return to the streets and cycle paths.
The alternatives are to let the 'arms race' (bigger faster ebikes) and carnage continue, or do what other cities have done and ban ebikes and bikes from downtown (more cars would be the pattern, not desirable), or let the old bikes die through natural wastage (bureaucratic and uncontrollable).