You can consider that the hasing power from China is bigger than everything else because it's the most overpopulated nation from everyone else.

Therefore you will have more people doing "stuff" for cryptocurrencies than on other place.
Not only that but their economic growth and technology involvement is way bigger than any other Country.

Based on those points you get your answer on why hash rates are bigger there.
Also making some laws against bitcoin or any other crypto doesn't relate the fact they can or not do hashing.