Steam, GameStop, Toys-R-Us, Walmart… Someone always makes a profit on selling games, or any products - even digital. Steam has not reinvented the wheel here. It’s not a new concept. Are you arguing that the idea of stores should be eliminated?
In return, the game is more likely to be seen, just like placing a product in a real store where people walk by it. It also gets advertised, reviewed, has another community outlet, and Steam uses their own servers and bandwidth to distribute it.