I agree with user above, Brazil president don't want to look weak in this situation. Especially after his recent conflict with Macron. But I think such decision made by him can make things even worse. Accepting help in such situation is normal things and lot of countries around the world helps to other when something terrible happens - big fires, earthquakes, floodings and etc
These news reminds me another recent story about Sibir forests fire and when Putin rejected to accept help from Trump.
It's bad that politicians first think about their ratings, political situation, but not how to solve problem.