some tables cannot cache to buffer pool

I have import some tables to DB by impdp. So strange, none of these tables cached to the buffer pool.

  SELECT o.owner, o.object_name object_name, o.object_type object_type, COUNT (1) num_blocks

    FROM dba_objects o, v$bh bh

   WHERE o.object_id = bh.objd AND o.owner NOT IN ('SYS', 'SYSTEM')

GROUP BY o.owner, o.object_name, o.object_type

ORDER BY COUNT (1) DESC

<== I saw nothing

I try to clone a table within same schema and select it.

create table afac01.fas_func_test as select * from afac01.fas_func;

select * from afac01.fas_func_test