Its the only choice available because the previous means of survival was at best subsistence farming. And it isn't guaranteed to happen, but impoverished countries will never enter modern society if they are just isolated from it for labor protections sake.
The trickle of money from the pockets of capitalists into the dictators of Indochina in exchange for functionally slave labor is still better than if these countries had nothing to offer the world at all.
You would want the optimistic capitalist means to uplift the third world to be simple investment - you take a country with nothing to offer and no resources, invest money in it to educate its people and develop its infrastructure, and then you would have their substantially improved productivity to profit off.
But that has never happened on just the backs of dollars because there is no way to risk manage that kind of arrangement. It almost always comes second to bombs or prophets as a way to provide that collateral - even if the country fails to recoup the investment, you can pillage the natural resources or convert its people into adherents of your own culture. Because those acting in self interest are approaching a scenario where the other party has nothing to offer (except idle hands) and you have everything.
It does not help laborers anywhere in the world to exploit labor and further weaken places where labor has already organized and achieved protection.
This is a fundamental failure of capitalism and a particularly harmful neo-liberal belief.