Why is there no "approval" for EASA Regulatory training organizations?

Because as EASA or other applicable jurisdiction Compliance or Quality Manager is usually responsible to determine that the provided “training standards” fully meets the requirements of the organisation itself?
This responsibility essentially accepts that the organisation itself is responsible for and manages the competence of its staff to ensure they are able to deliver their required role in the most effective way. (This includes any required recurrent training for example).