It's worth noting that car registration in Shanghai was staggeringly expensive before electric cars were a possibility. That's just a continuation of existing Chinese policies; it obviously helps electric cars, but that was no part of the intent of the policy. (I assume the intent was some combination of reducing traffic times and reducing pollution from exhaust.)
The support by local governments is a major factor for the EV boom (along with other booms like renewables).
The mixture of federal, regional, and local support is a fairly critical part of the Chinese development model.
(Technically there's no federal government, period. There's just the bureaucracy and the party. The party's leadership determines policy, the bureaucracy carries it out. Local decisionmaking exists when micromanagement reaches its limits, and ultimately it is a system of gap-filling. Or, in a sense, it's a system that the 9th and 10th Amendments of the US Constitution anticipated and therefore needed to be addressed, 200 years early)