It's a problem of market oversaturation. A casual gamer only buys about 2 games a month. A hardcore gamer buys about 10 games a month. Which means that your game has to be one of the most interesting games (out of 1000's of games) for someone to want to buy it. On the other hand, if someone wants to buy a bottle of pepsi, they buy about 2 bottles of pepsi a day. (But it's actually a worse monopoly, because there are only 10 or so major pop brands availiable in common stores.) In any case, it's like a barber shop. Barber shops are localized and depend on the town. But in games you have to compete with the entire world. More stuff to compete with.