[WaxProlix]

Large parts of AWS don't run on AWS either, due to issues with circular dependencies and similar problems. Similarly, if all of AWS onboards to use your AWS service, suddenly that's the business. Your 'real' customers and their traffic are dwarfed by the rest of AWS, making it hard to keep those real customers at the forefront. There's also an issue with those deps of cascading failures; having two separate fabrics/strata for internal and external offerings is similar to having a multi-regional offering in that it's more robust to random failures and such.