Valve is not a public company so there is no shareholders nor investors who can pressure Gabe to sell. There is also absolutely no insensitive to sell for him. Even if he gets tired of Valve he can simply start a new venture by using the insane cash-flow raining directly in his bank account.
Because most companies hemorrage money. Valve was built after Gabe and the other co-founder got rich as hell from working on microsoft. They didn't need funding while valve was bleeding cash, so they don't have to do that.
