Why on earth would countries want to limit improvements? We don’t see countries engaging in vaccine non-proliferation agreements, even though those are unevenly

Why on earth would countries want to limit improvements? We don’t see countries engaging in vaccine non-proliferation agreements, even though those are unevenly distributed. Non-proliferation is for destructive technologies. However, as stated in a sibling comment, I think the advantages gained from IQ gene editing are quite exaggerated.