Just for example, take the biggest benefit claimed in the letter of 122 million children saved. It seems to suggest that it's because of their work. Has nobody else anywhere , including those in the affected countries done anything to save the children. Why do they or anybody think that all of this can be attributed to to the Gates foundation!!
Moreover as the Gates foundation is focussing on childrens' lives, does it make any sense for anybody with lesser resources than them to tackle this problem? There is no chance of getting any recognition, as Gates foundation will claim it and it will be hard to argue against as well.
These are not my views, I'm just saying that it's possible to have these thoughts if you are cynical.