Good here doesn't mean the music is to your tastes, or has some subjective level of sophistication or technical prowess.
The objective measure of how good it is can only be compared using commercial successfullness. If sufficient people are willing to shell out for the music, then it must mean it's good.
Because the assertion that good musicians are rewarded is unfalsifiable in that formulation. Your definition guarantees that you will always find it true. It proves nothing.
