It has more to do with economic conditions I believe. Here in India it's the same, most people get into software engineering because of easy availability of jobs and don't really care about Computer Science itself. So the concept of Open source feels alien to most engineers here, especially "working for free" when you have to struggle so much just to get a very basic salary.

Also who has time for side projects when you work in the 996 work culture.

I don't think this can be generalized for China. Plenty of companies in India, Japan and US have the same shitty culture too. Tesla, Space X, Apple are infamous for such workaholic cultures.

Products get cloned almost immediately once released in the Chinese domestic market, especially when there's a potential for them to make money. It's about keeping the IP as closely guarded as possible while attracting users.

Companies are very conscious of copying and they see open source as only facilitating that - the cons outweigh the pros. Tech savvy consumers don't appreciate that a company has open sourced some of its work because there's no culture of open source, and the act of open sourcing only allows competitors to rip something off easier. Why would they?

If there's no expectation of anyone contributing back, it makes sense.

OTOH I wonder how Vue.js, Cocos2D, echarts, etc even survive in this circumstances — these seem to have some contributors beside the original authors.