What I also find interesting is the fact that Netflix doesn't necessarily even need the "flex" to succeed. Their push on bird box could have failed miserably, and they really wouldn't have suffered greatly, whereas Disney's push of A Wrinkle in Time probably hurt, since the movie ultimately flopped and their only chance to recoup costs was after the huge investment.

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.