This article on their blog gets into the compatibility that cockroachdb offers and why they even decided to do that in the first place: https://www.cockroachlabs.com/blog/why-postgres/

It's also very useful to be portable across many cloud providers (in addition to on-premises), which is what crossplane is providing for your apps. In terms of databases, Amazon RDS, Google Cloud SQL, and Azure PostgreSQL are all abstracted away from the developer so that their application should work across those without changes as well.