Additionally, businesses will not only sell Sony codes. They won't be like car dealerships, tied to 1 manufacturer. Due to this, they'll have even greater incentive and negotiating position to pressure Sony as if Sony doesn't want to play ball, the sellers can start promoting non-Sony products to consumers.
With direct sales only, Sony can have perfect vertical integration: they make the console hardware, they make the custom OS, they own the game publishers, they own the developers, and they own the store that sells games too. That's beneficial only to Sony.