It encourages the idea that the score of a win matters. Think about that. That's like saying, Tom Brady's "rating" should be based on by how much he beat other teams. He has won 6 super bowls. But most of them are in a tight fashion, not in blowouts. I shouldn't be rewarded more or less for a close win vs a "decisive" one. The score doesn't tell the story of a match, and at the end of the day, winning is the most important thing, not killing your opponent.
So obviously the number of games has to be factored into a system that has competitive matches as one of its main goals.