Why "SET CONTAINER" system privilege does not work ?

## I connect to a pdb named orapdbb with user b_admin who has been granted the "PDB_DBA" role
SQL> show con_name

CON_NAME
------------------------------
ORAPDBB
SQL> show user
USER is "B_ADMIN"
SQL> select * from dba_sys_privs where grantee='B_ADMIN';

GRANTEE
--------------------------------------------------------------------------------
PRIVILEGE                                ADM COM
---------------------------------------- --- ---
B_ADMIN
SELECT ANY DICTIONARY                    NO  NO

SQL> select * from dba_role_privs where grantee='B_ADMIN';

GRANTEE
--------------------------------------------------------------------------------
GRANTED_ROLE
--------------------------------------------------------------------------------
ADM DEF COM
--- --- ---
B_ADMIN
PDB_DBA
YES YES NO

## The "PDB_DBA" role has a privilege called "SET CONTAINER"
SQL> select * from dba_sys_privs where grantee='PDB_DBA';