Either way its still only around $10 per book (20% of $50, 50% of deep discounts on Amazon so maybe $13. I don't think 5E has sold a million units yet due to Mearls not mentioning it since he has claimed it has outsold everything apart from BECMI and 1E. If it had sold 2 million for example they still have only made 20 million dollars over almost 4 years from the PHB which we all know is the biggest selling D&D book. If D&D is getting 20-30 million in revenue WotC is making (at best) 6-15 million dollars plus whatever they get off the games and VTT.
Its still a nice amount of money but a decent movie or video game is 10 or 20 years profit in one hit. The problem being that a decent movie or game is going to eat huge a huge amount of money and its not worth paying WoTC licensing fees to make a decent game or movie. An average priced game is 80 million, a cheap movie is still a few tens of million and a D&D movie will need some costumes or CGI.
5E is doing really well by D&D standards but I think some people get carried away with what it is realistically making. It not really doing that much better than say 2E but back then a great game could be made for less than 1 million dollars or you could get the movie license for 10k IIRC.
A good D&D game by default has to be an indie game.