Amazon's record with OSS contributions is notoriously poor. For example, see their refusal to allow their query routing extensions to pgbouncer to be used on anything other than AWS:

https://github.com/awslabs/pgbouncer-rr-patch/issues/3

There's certainly room to criticize Elastic for their approach to OSS and/or their response to Amazon here, but Amazon's "open-sourcing" of a bundle of the OSS bits of Elasticsearch plus a few third-party OSS plugins is nothing other than self-serving, opportunistic PR.