1) They genuinely want (and believe it is actually possible to achieve) an international agreement and governing body to “pace” AI development — and believe that governing body will be successful in doing so.
or
2) They see an opportunity for regulatory capture that grants them a stronger incumbent position and control over future AI regulation.
… and those submarines only represent about half of our deployed nuclear arsenal.
We only agreed to nuclear arms constraints that left us with civilization-destroying capability, preserved our ability to keep improving and modernizing that arsenal, and locked out non-nuclear powers from development (and didn’t fully succeed at that).
Does that seem like a successful analogous example to you?
If anything, it’s a much better analogy for regulatory capture and incumbent entrenchment, not successful “pacing” of dangerous technology.
Theoretically, Trump or Putin could do it by pushing the nuclear button. That will only cause around 4 billion deaths, and it's very likely to halt all AI development, so it would be a great success (infinity times as many survivors as the business as usual option).