Amazon's behavior may feel exploitative, but it isn't. That would be like saying Red Hat is exploitative.

Part of the whole concept of free software is that you have freedom of choice with vendors (this is derived from "freedom 0"). Amazon is providing the software and its support as part of the Elasticsearch offering as a managed service. Elastic is a competing vendor, both as a managed service and in a traditional sense too.

Elastic made this decision because they wanted to be the exclusive vendor for Elasticsearch. That's fine, but it's not in the spirit of free software.

If anything, Elastic has exploited the third-party contributors who contributed to Elasticsearch under a CLA by promising to not do what they did and then blaming AWS for doing it anyway.