I disagree. There are more and more services providing logistics, delivery, payments, etc. And they are quite reliable. Just 2 years ago I was entirely relying on Amazon as a good ecommerce. As of 2020/2021, to be honest, there is nearly no difference with some individual retailers (which don't use a 3rd party platform to sell their goods like Amazon or Ebay). Lots of websites have improved, logistics, delivery, customer service, payments, ..etc etc. They key, in my opinion, was the logistics + delivery. That's what Amazon was exceptionally good at. Now that the infrastructure is nearly the same for everyone, why would you share your profits with Amazon and risk to be out of the business in 1-2 years?