Scientists are part of a worldwide community because they don't find many people who really understand what keeps them awake at night. If only three people really can understand you, then it doesn't matter from which part of the world they come from. This was even the case with scientists from the US and the Soviet Union working together in the coldest days of the cold war. Scientists share knowledge and tools, and in this case the cell lines are tools. For example, a cell line with cells that have much more ACE2 than normal makes it easy to test if a virus uses ACE2 as entry point, it will infect these cells faster if so. More important than the scientists are the sponsors because they determine the direction. Some of them wanted the scientists creating SARS version 2.0, and they were successful.