My takeaway from Bird Box is that if Netflix wants to make any of their original content one of the most-watched media events of the year, they can do it, regardless of the quality of the content itself. All it takes is for them to slip it in to people's "custom, curated" lists at a higher frequency, and maybe do a little subtle social-media engineering on Reddit/Facebook, and bam: instant box office smash of a deriv…
Netflix's goal is quite distinct from much of its competition. In simplistic terms, their goal is to release enough compelling content to keep existing subscribers subscribed and then hopefully entice new users to sign up more than old users quit. These "flexes" I would assume are primarily for the second category. If you make something enough of an event, with subscribers talking about it all the time, maybe non-subscribers will think they are missing out and take the plunge. If that fails, however, they only really lose out on the marketing costs, since it's very unlikely to affect the existing subscriber base at all.