It doesn't make sense financially. Arrival had a budget of $47m. The general rule is that marketing budget for a movie is 50% of the production budget. That leaves us at $70.5m to break even. At $15 per month, you need that movie to generate 4.7m new subscriber-months to be worth it. Is releasing Arrival on HBO Max going to be the deciding factor for 4% of US households to subscribe for a month? I doubt it.