Row level security implementation in Foreign Table in Postgres

Row level security feature implementation in Postgres is through policy and the row security qualifier is attached as a
subqueryto the main query before query planning. The RLS is implemented through ALTER TABLE STATEMENT.  
But my doubt is why this feature is not enabled in case of Foreign Table. (ALTER FOREIGN TABLE doesn't have a option of
enablingRow Level Security).  
Is this is not implemented due to some limitations in the current design?
Because from a quick view it looks like the security subquery can also be easily attached to the main query and passed
forprocessing in foreign database.  

Thanks
Sounak