The Vow on HBO — have popped into the larger cultural conversation, in ways that keep encouraging showbiz executives to hire filmmakers who want to tell stories drawn directly from reality. For the streamers, documentaries fill a need. Netflix’s programmers in particular like to overwhelm subscribers with options each month — to keep the customers in the store, so to speak. Docs are both relatively inexpensive to make, and potentially limitless in scope. Deeply into politics? Love music? Fascinated by true-crime stories? Netflix has the inventory to cover just about any interest. (True crime especially… scarcely a month goes by without a new non-fiction murder series hitting the service.)