That is true for all consolidated markets. Everyone could in theory create a service to compete with Amazon. There is really nothing preventing people from doin

That is true for all consolidated markets. Everyone could in theory create a service to compete with Amazon. There is really nothing preventing people from doing that apart from the fact that it is extremely difficult to penetrate that market. In this sense those are walled gardens, but because of the nature of those markets. E-commerce, telecommunications, datacenter, banking to some degree are all examples of hard to penetrate markets. The original article goes on to explain that going head to head against solutions that are consolidated in these market are a waste of time and money. Better to find and exploit a niche that is still untouched.