Because USA prohibit China from participating in any International Space Station project.We have to build our own space station.

The ISS will be retired in 2024,then China Space Station is the only one in the world.

No prohibit can stop China‘s step,Shut China out only leave you behind.

You should know the fact, in the past 5,000 years,China has lead the world in 4,800 years except the latest 200 years,Now China is retaining to its position.