If I'm not buying from Amazon I have no reason to shop there. Its just another marketplace and I like ebay a lot more for that.
It's the difference between a chain coffee shop in a bookstore being staffed by employees of the bookstore, or being staffed by corporate employees of the coffee-shop chain. Either way, you can go into the bookstore and get coffee. It's just a matter of who's getting the profit margin and dictating sales deals.
Also, most big-ticket name-brand items on Amazon are already sold by their manufacturer, because that's a better deal for the manufacturer. For example, iPhones on Amazon are sold by Apple, because not even Amazon has enough bargaining power to get wholesale prices from Apple. This has always been the case. It's only the medium-sized businesses, large enough to matter to Amazon's bottom line, but small enough for Amazon to bully, that Amazon was acting as a middle-man for. They're giving some of that up, because the profit margin they were capturing as a middle-man, which was previously enticing to them, is now too slim to matter to them.