Because PostgreSQL major version upgrades are hard and for large databases, requires some level of downtime. Given that that major version releases are on an annual release cycle, staying evergreen is really really annoying.
Under some elementary scenarios (and using some Postgres offerings), you can do a full major upgrade using logical replication (even with replicas). It depends on your situation, generally I agree, any sophisticated use of Postgres (lot of views, materialized or not, fast changing schema, large objects, and so on) makes upgrades a pain and is generally somewhat of an unresolved problem in my opinion.
Agreed. I also see PG 16 is scheduled for release later in the fall. Also, you don't want to put the first 16.0 version on a production system, rather wait until 16.1, 16.2 etc.
