There are many options available with PostgreSQL you could also do a physical full backup + WAL level replication to keep key AND a get low downtime. What migh

There are many options available with PostgreSQL you could also do a physical full backup + WAL level replication to keep key AND a get low downtime. What might have oriented theirs choice is that they wanted to upgrade from major version 11 to 15 during the migration process. This is only available using logical replication. Otherwise you'd have to chain upgrade process of each major version (and possibly OS because 11 is EOL on some arch) and this is nor trivial nor quick.