If that's the case, then why does other country have their NBA players still play for the upcoming FIBA world cup? They should have also been restrained from participating too since they have obligation in the NBA?
Those who want to participate in the NBA will do that and those who want to play for their country in the world cup has the choice of doing that. Players such as Giannis Antetokounmpo of Greece have opted for the world cup, but most of the American heavyweights (including James Harden, LeBron James, Williamson, Lillard, Curry, Irving, and Kawhi Leonard) have opted for the NBA. It's just a personal choice.