Undoubtedly this is because the US approaches deproliferation with a “you first” mentality, and then once the other side starts, the US says “jk lol.” The US can’t be trusted to hold it’s end of bargains like this so why would a serious country entertain talks with the US like this?
That’s okay the free market will fix this by destroying society as we know it leading to the next great mass extinction of which humans will be a part of. It’s not a big deal really.