> If they aren’t open sourcing the innovations they make on top of open source software

I'm not sure I'm reading your statement correctly, but it sounds like you're saying that anything not developed under a copyleft license is proprietary.

If it was important for authors to receive contributions from derivative works, why would they have selected a license that doesn't require that?

I don’t see how you interpreted it that way - anything released with a proprietary license, or closed source and not released at all, is proprietary. The fact that it’s derivative of an MIT or similarly licensed work makes no difference.

Yes, sorry, I thought you were giving it a normative interpretation, but you were just stating a fact.

I agree that your statement is correct.

The innovations Amazon ads are useless outside of Amazon. Everything is about scaling open source systems inside of the Amazon ecosystem. It's not going to be usable or useful anywhere else.

That’s difficult to discuss without knowing the details, but it’s hard to believe that there isn’t anything that is of use to someone outside of amazon, even other cloud providers. There must be some efficiency gains somewhere that would benefit the original software.

Maybe minimal benefits to other cloud providers, but hardly something you'd need in the core library. I think Amazon should contribute more to open source, but I certainly wouldn't think any company should release something that would only benefit it's competitors.