But at least they maintained the courtesy of major version filesystem compatibility allowing faster in-place upgrades during an extended period (from v9.0 - 9.6), by simply changing the binaries. Possibly that held them back, but yearly updates that require more downtime/reindexing isn't so much fun, and possibly the reason why many sites skip upgrades until previous versions drop out of support (esp AWS RDS users). While the alternative of a logical replication upgrade (from v10 onward) has availability benefits, its a major project with unavoidable costs and significant risks unless schemas are relatively simple.