Disclosure: I work for AWS, but I do not work directly on Elasticsearch related services.
Elasticsearch is/was an "upstream" for Open Distro for Elasticsearch (which is a distribution / collection of software). As an "upstream", changes to the core Apache 2.0 licensed software was sent as pull requests to Elastic, which are usually merged. It isn't correct to say that AWS has not been contributing to the upstream Elasticsearch code under an Apache 2.0 license (and, also, signing the CLA to boot, which allows Elastic to relicense AWS contributions under SSPL).
Here's a sample of PRs from AWS developers that I could find: