The problem for them is that China is smartThe US and EU wanted to work together to slow down China. China slowed down and again its not good.
When China gets slowed down, the first thing it does is blocking exports to satisfy domestic demand first. Its not a muppet which would deprive its domestic industry of key supplies while exporting these same supplies to the EU/US
The same is for here as well. China is 100% focusing on shifting magnesium towards domestic industries, and if anything is leftover it will be exported to the world