A nuclear arms reduction treaty ensures that all parties keep their own relative power (that is not dictated by the nukes) without going into a boundlessly expensive arms-race that would bankrupt all of them.

A prohibition on cyberweapons exports doesn't have any similar impact. It wouldn't even make defense cheaper. It's something that may be useful for civilians, but how often do civilian concerns enter those high-level treaties?

(Anyway, I'm not even sure it gains us anything. The absence of somebody exploiting them does not make the vulnerabilities go away. What would really help is if some moderately advanced country decided to take their head outside of their ass and do something to protect themselves. But I don't expect to actually see that happening, everybody only wants to work on the offensive.)