The all-or-nothing nature of the PDB API makes it difficult to allow others to integrate with it for security conscious customers. The PDB CLI lowers the bar for this to be found by customers. Even getting read/write access control would be a good start rather than aiming for deeply detailed query controls.
RBAC allows customers to delegate, because there isn't any actual control other than can you access it or not it makes it more difficult for them to delegate as they often can't trust others to not abuse the full access.