This American Life isn't one of the primary NPR podcasts to which I listen, but if it follows the trend of other NPR podcasts it probably draws more heavily on subject matter experts (e.g. university professors) and leadership positions in private enterprises than the rest of the population. These occupations, at least the latter, are disproportionately occupied by men. One could argue that the bias towards subject matter experts is sexist, but that seems fairly weak and indirect unless it can be demonstrated that the choice of interviewing these people is motivated by a desire to interview more men than women. One could also argue that the podcast should stop its focus on subject matter experts - but that would fundamentally change the nature of the podcast, essentially making it a different product.
In fact, that's possibly the next move for TAL in the wake of this study: asking themselves, why is our staff choosing the guests that we are and what opportunities do we have to go afield and find someone fresh?