With OpenSearch, you can start your own community and drive it, whereas with Elastic you can't unless you're willing to promise your fork won't get resold as a hosted service.
In all seriousness, is Amazon good about accepting PRs and stuff from volunteers for their oss projects (i.e. Firecracker)?
So far, Amazon have been good about accepting PRs from volunteers (I can only vouch for the OpenSearch project) and have committed to moving to a more open source model with active maintainers from other organisations. It's early days but it looks healthy so far.