It seems that Amazon have quite strong internal standards for services that they're going to roll out, for example all critical services are required to use Dyn

It seems that Amazon have quite strong internal standards for services that they're going to roll out, for example all critical services are required to use DynamoDB, which would make it difficult to integrate a competitor into their wider ecosystem of AWS services. They've also got a vast pool of people to draw from around the company which allows them to implement new functionality on top of existing tools they've already built, rather than having to do everything from the ground up.