AWS does not develop .NET SDK, as I mentioned in my earlier post there is no contribution of AWS in development of .NET, so they just provide infrastructure support of what ever Microsoft and the open source community releases.
In general microsoft acts as a steward to develop .NET and related infrastructure on Azure, then AWS copy and launch it as .NET infrastructure as service. They play catch up with Microsoft in this area.
I will stand corrected if you can show me that AWS (i.e. Amazon) has active open source .NET framework core developers in their internal team developing and enhancing .NET SDK or CLR open source versions.
They do the same with AI and ML Services. It is built using TensorFlow, sci-kit learn, pytorch, CNTK and various python and C++ open source libraries. Again I have yet to see example of AWS (i.e. Amazon hiring core developers of these libraries and release open source versions). They don't develop these libraries just leech on it to create it's own API's. I have yet to see any framework from AWS like TensorFlow, Keras, Pytorch and CNTK.
There is nothing to copy as far as .Net. Microsoft releases a new version of .Net, all AWS has to do is make sure that its SDK’s support it. But there usually aren’t any breaking changes.
As far as the other services that I could see needing to support, the only ones that I can think of is CodeBuild and lambda. For those two, you can create custom Docker images and runtimes respectively.
And the other question, are you a .Net developer?
How does open source help an end user who is deciding which cloud provider to use?