If Games Workshop decided to massively pull back on Space Marines, outside of Horus Heresy, would it be a net positive for 40k?

Chaos, Xenos, and the other Imperial Factions have either been chronically under-developed, or grossly outsold even in the rare situations where they weren't. How have we, as a consumer base, been so complacent as to allow Marine players to single-handedly dictate both the direction of the setting and the game?

pic unrelated