They were in talks to participate in the ISS. The ISS partners invited them in as potential responsible, collaborative partners in the future of manned space flight..
Then they conducted a reckless ASAT test at relatively high LEO altitudes and nearly doubled the number of trackable debris at that altitude [see Johnson Space Center's Orbital Debris Quarterly Newsletter for the chart]. At that altitude, the pieces of their defunct weather satellite will remain a hazard for many decades. That got them uninvited.
China needs to decide whether the PLA is running the show or not, and decide whether they want to be a responsible space-faring nation... or not.