Perhaps it is simply a question of balance, or of longing: there is SO much fiction available to us (and so much of it is the same, or at least so similar), tho

Perhaps it is simply a question of balance, or of longing: there is SO much fiction available to us (and so much of it is the same, or at least so similar), those who want the traditional benefits, if you will, of fiction - escapism, experiencing the perspective of another, etc. - are more likely to find it in non-fiction narrative than in fiction. And not because these things are no longer found in fiction but that so much fiction is formulaic and familiar that the odds aren’t there. Curating a set of non-fiction narrative to find the gems is simply likely to take less effort and to yield more results. Consider too that writers of narrative may well have an advantage in finding an authentic voice, since their narrative is theirs, reflecting their unique experience, where fiction (typically) tries to find common ground.