IMHO this "almost open-source" is even better because otherwise people wouldn't be willing to start companies around their open-source solutions knowing that AWS would just offer a hosted version and screw them over.
[1] https://www.nytimes.com/2019/12/15/technology/amazon-aws-clo...
[2] https://aws.amazon.com/blogs/opensource/setting-the-record-s...
So much wrong in this world that we can't predict and handle ahead of time.