Cheap digital PS3 games - Where do they come from?

I've been asking myself where do digital PS3 games come from, I'm just wondering how do they do that if you download those games from de PS Store anyways, they are just like sharing a game with you. You pay for the game, they send you an account, then you just create a new user profile and log in, you go to the store and re download the game from the store, you will have to keep the user profile, but you are able to play with your account on any other profile. I bought GTA V that way. I've bought those games from web pages and games are way cheaper than buying them directly from the PS store. Just so you get what I'm asking: Black Ops III is 60$ and buying the game from that page would just cost you 12$. How does that work?