They're making money off of a game that quite obviously is putting "GTAV" in it's name so that more people see it, and some of the trailers use GTA footage n stuff. Dunno.
If you read just a little bit on the page, you'll note that they say, and I quote:
"100% of the profits from this game go to young people’s charity Peer Productions. Without Peer Productions the NotGames team would never have met. By buying this game you can help us pay something back."
What jackasses these guys are.
Here is a link to the charity they refer to. It's a small time UK charity devoted to helping young people develop skill in performing arts.