USAIDS assistance for Zambia was 13 million USD, or about 0.12% of their government budget, or about 1.2% of their health budget. AIDS assistance comfortably fits in their government budget.

Let's face it. Trump made them choose to give or deny AIDS treatment to the poor, at a minimal cost to them. There were no real budgetary consequences to the Zambian government to do it. Relatively speaking it costs Zambians more than it would cost the US, but it's still not much, not to them either.