Why am I getting permission denied on an ownership change? My current user is pronto

mediapop_staging=&gt; select current_user;
 current_user
--------------
 pronto
(1 row)


This user a standard super user created on AWS RDS.

mediapop_staging=&gt; \du pronto
                        List of roles
 Role name |          Attributes           |    Member of
-----------+-------------------------------+-----------------
 pronto    | Create role, Create DB       +| {rds_superuser}
           | Password valid until infinity |


But I'm getting this:

mediapop_staging=&gt; REASSIGN OWNED BY pronto TO mediapop_staging;
ERROR:  permission denied to reassign objects


Why? How can I resolve it?
There are some unintuitive permissions requirements when using REASSIGN without a superuser.  See this other pots where I answered the same question: https://stackoverflow.com/a/62557497/79079