Because there is less competition. Open game stores are flooded with games, mostly of low quality. It makes it very hard to stand out and you just fall off the front page really fast. There is too much noise and everything gets the same billing regardless of quality, unless you hit a top sales spot. However, top sales spots frequently have less to do with quality and more to do with appealing to the lowest common denominator.
Just look at the ios app store, the top is generally freemium games or games that are actually thinly veiled skinner boxes with some nice art. Either that or casual games that have broad appeal because they are simple games.
On Steam you get top billing for at least 2 weeks after release.
Some open store examples: Desura, Indievania, XBLIG, android, even the mac app store is pretty open compared to Steam.
Just look at the ios app store, the top is generally freemium games or games that are actually thinly veiled skinner boxes with some nice art. Either that or casual games that have broad appeal because they are simple games.
On Steam you get top billing for at least 2 weeks after release.
Some open store examples: Desura, Indievania, XBLIG, android, even the mac app store is pretty open compared to Steam.