I don't know what's going on behind the scenes, but if I were to speculate, they probably have a contingency plan for this scenario which involves concessions from those countries if they default. Maybe land or mineral rights, maybe something more complicated. That's just a guess from my side though.
I suppose the "contingency plan" was the main plan all along.
It is easy to bribe or to force governments in poor countries to take a loan in disadvantageous terms. Public servants easily do actions that will have consequences in the long term for a bribe, since when the concequences will reach, they will be gone already.
