When you get as big as Amazon it's reasonable to expect some concessions to the people who use your platform, just like if you get as big as GM your workers will want to unionize.
This really isn't all that different than what Walmart has a history of doing. Become your biggest source of business, then force you to lower the price or lose it all.
If your supplier raises prices you can become unprofitable, if your distributor changes policies you can become unprofitable, if FedEx raises prices you can become unprofitable, if price of gas goes up you can become unprofitable, if your rent goes up you can become unprofitable, if taxes go up you can become unprofitable, if laws change you can become unprofitable, even if a local employer closes you can become unprofitable, if a competitor comes in and undercuts you you can become unprofitable, etc.
It's not fair to criticize a small business for not building up, from scratch, the infrastructure and customer base that Amazon has. Especially when many of these small businesses wouldn't even be feasible without Amazon's infrastructure.
Amazon is basically a monopoly, I'd like to know how you imagine a small business competing against them. And why should a small shoe/fidget-spinner/alibaba-reselling business need to build their own shopping website anyways? "Platforms" should be free.