> But then why are posters above pretending that many countries, which signed up this IP regime under threat fo being cutoff from trade, didn't do that under duress?

Because most people reserve "duress" for a threat to one's rights. In the case of nations, these rights are generally territorial integrity (basically, the right not to be invaded or attacked) and political independence (the right to self-govern, including to choose with whom and under which terms a nation engages in trade or other treaties and alliances). While there are certainly powerful incentives for cooperation, it's incoherent to argue that exercising one's right to self-govern is coercive and thus out-of-bounds.