nothing is literally stopping them besides a deep understanding of what it takes to make companies that can last a hundred years
amazon ruthlessly drives down costs because they know the moment they leave the door open too far, someone will eventually come in and supplant them
an example is how SQS has gotten 99% cheaper since it launched
bezos is the one who said "your margin is my opportunity"
they can one day turn around and start cranking up prices but this is how the last generation of companies (Oracle, IBM, etc) died