The point in this case isn't drought resistance, it's increased yields for what does grow. If food supplies are low, higher yields from pest resistance become even more important.

And even if resistance has been developed in "parts" of the US corn belt, presumably that would take years to develop in Kenya as well, in "parts"?

Better irrigation and cassava might be great ideas too, I wouldn't know. But it doesn't seem either/or -- why not try GMO maize as well?