AMF is not usually justified from a long-termist point of view, so it is not really surprising that its benefits seem less obvious when you consider it from that point of view.
I agree in principle. However, there are a few other reasons why I believe making this point is worthwhile:
GiveWell has in the past advanced an optimistic view about the long-term effects of economic development.
Anecdotally, I know many EAs who both endorse long-termism and donate to AMF. In fact, my guess is that a majority of long-termist EAs donate to organizations that have been selected for their short-term benefits. As I say in another comment, I’m not sure this is a mistake because ‘symbolic’ considerations may outweigh attempts to directly maximize the impact of one’s donations. However, it at least suggests that a conversation about the long-termist benefits of organizations like AMF is relevant for many people.
More broadly, at the level of organizations and norms, various actors within EA seem to endorse the conjunction of longtermism and recommending donations to AMF over donations to the Make-A-Wish foundation. It’s unclear whether this is some kind of political compromise, a marketing tool, or done because of a sincere belief that they are compatible.
The point might serve as guidance for developing the ethical and epistemological foundations of EA. To explain, we might simply be unwilling to give up our intuitive commitments and insist that a satisfying ethical and epistemological basis would make longtermism and “AMF over Make-A-Wish” compatible. This would then be one criterion to reject proposed ethical or epistemological theories.