The amount of new gamers is not making up for the amount of new games.
Consider Call of Duty for instance. Say there are 7 billion people on the planet, and say they are all gamers that are willing to equally divide themselves up for each game out there (not realistic as the newer games would get more of the audience but bear with me). The first Cod, all 7 billion people play it. The second CoD, there are now 100 million new people, and 3.55 billion people play it while 3.55 billion people play the first one. The 3rd Cod, 100 million more people are now gamers and about 2.4 billion people play each one.
Now consider that in reality, the new games take up most of those gamers, more than one big game comes out each year to take away players, people stop playing video-games, and we don't have nearly as much as 7 billion gamers in the world. Even a new game will eventually get overlooked as soon as the next one comes. Sure, more people are here than 10 years ago, but the amount of games has outpaced the amount of people per games.