There might be a small percentage of people nihilistic enough to want to unleash a truly devastating bioweapon, but basically everyone wants what AI has to offer.

I think that's a key difference as well.

And how would a treaty like that be enforced? Every country has legitimate uses for GPUs, to make a rendering farm or simulations or do anything else involving matrix operations.

All of the technology involved, in more or less the configuration needed to make your own ChatGPT, is dual use.