Because penalties for non-compliance are how mandates are enforced; otherwise, they aren't mandates.
What you probably don't understand is really why is the penalty not immediate termination, or termination after a certain period of delinquency, not why there is a penalty, and I suspect it actually is the latter, and the downgrade in internal rating is the immediate and automatic consequence of delinquency (also, I don't know how Perf works, for all I know the stated downgrade may be enough to normally trigger being put on a PIP and terminated if the problem isn't cured quickly.)