As I see it, we have these open-source / core products, and the companies maintaining them are looking to provide certain value-added features (particularly critical to the enterprise crowd) in exchange for some vendor lock-in.
- Amazon's tactics are to either offer a proprietary alternative to those enterprise features (Elasticache, DocumentDB), or to vend a competing open-source alternative with the aforementioned features (ElasticSearch, Corretto)
- Google's approach looks to be partnering with the maintainer to offer a shared walled garden (so while you're still locked-in, you can easily migrate between blessed partners).
I'm not yet convinced GCP's tactic is overall good for opensource as a whole, since they are setting themselves up as de facto benevolent gatekeepers; although admittedly they will allow these projects to thrive under their current stewardship in the medium term.
Edit: I'm also interested in seeing what happens here when there are multiple competing vendors who have equivalent claims to stewardship of the underlying project - ex:- Hortonworks and Cloudera pre-merger, or Cloudera vs. MapR. Also, how vendors with vast proprietary ecosystems work out in this "native fully managed" setting, ex:- Databricks which has managed to get on by on the Azure and AWS marketplaces.