Didn't a ban on space weapons forestall the weaponization of space by a few decades?
Didn't bans on chemical and biological weapons keep research in those fields small enough to prevent the emergence of politically potent factions with a pecuniary interest in their development?
The nuclear test ban treaties have held up well.
There is a big difference between "states openly develop these things and rich people lobby for more budget", and "states have secret programs as a hedge against noncompliance by the other side".