Shenzhen is huge and has an absurd amount of tech companies, so this doesn't really surprise me.

China's government is handing out massive subsidies for everything called robotics. This causes the number of companies that claim to do robotics to be inflated

industries tend to be more centralized in China. It's not that that's indicative of every city, more that Shenzhen already has easy access to the kind of manufacturing and products that a robotics company would find ideal.

the city is in key national focus for prototyping modernization and creating a smart city.

It must be easy to start a business there