The suppliers aren't stupid, they see where this is going. Any wholesaler who agrees to that clause deserves what happens next – being overtaken by their more forward-thinking competitors.
Not true, you'll find a lot of luxury goods have done this for years, e.g. high-end watchmakers. The only online retailers for them are websites of brick-and-mortar stores, or the grey market.
The name of the game is differentiation. There are even brands that are only sold door to door. I could very easily see brands that are only sold in stores.
The suppliers aren't stupid, they see where this is going. Any wholesaler who agrees to that clause deserves what happens next – being overtaken by their more forward-thinking competitors.