I guess these AI firms must've signed stacks and stacks of copyright leases to get where they are.

Simple, just follow the international rules. If you haven't registered your patent in a country, you don't have any patent rights there. If a company uses your patent and only sells its products within that country, you have no legal standing whatsoever, regardless of whether that country is China, Japan, South Korea, or even a European country. The same rule applies everywhere.