I'm not a geopolitical expert, but I'd imagine the main dynamic at play here is:
1) The US has strong influence in China's sphere of influence and doesn't want to give it up.
2) China wants to drive the American influence away from its borders and shipping lanes. They believe that very well could be possible in the coming years.
3) If you're China, you don't want to sign a weapons ban that benefits the incumbent.
4) If you're the US, you're not going to stop AI weapons research unless China does too.
1) The US has strong influence in China's sphere of influence and doesn't want to give it up.
2) China wants to drive the American influence away from its borders and shipping lanes. They believe that very well could be possible in the coming years.
3) If you're China, you don't want to sign a weapons ban that benefits the incumbent.
4) If you're the US, you're not going to stop AI weapons research unless China does too.