Having lived there, I can say there are a few reasons:

1. Chinese typically only read/write Chinese. Steemit is very English oriented. Hence the difficulty in language.
2. Various areas in China have Internet slowdown or complete blocking of various sites including steemit.com So if you were to use the site straight off a regular computer, it might not work at all or just load extremely slowly.
   This is not uncommon though as most Western sites such as google.com, youtube, facebook, instagram are completely blocked in China.
3. There are ways around no 2 but requires one to have a higher level of technical competency and understanding. e.g. using VPNs.
4. Chinese have their own alternatives from most sites and apps in the West. Chinese versions which are regulated by the government but have most or all of the features of their Western couterparts.