The 500 million isn't for the devs. It's for the game. Activision published DESTINY, therefore the money goes into the development of DESTINY. I'm sure Bungie pays their own workers, plus a bonus when the game sells. Don't forget that Bungie has been around for a looooong time, and has made one of the most successful franchises in....well not just gaming, in the history of franchises. I'd also be surprised if they aren't getting a bit of money from the newer Halos as well, considering they created Halo.