Sales tend to be proportional to the marketing budget. You see this in every entertainment media. Movies and Music, in particular, will have marketing budgets equal or in excess of the actual production costs.

It isn’t simply that 1% of the games make 110% of the money. It’s that 1% of the games get a marketing allowance at all, while the majority of indie projects and first round game offerings just get spat out into the void with little more than a whisper.