https://w3c.github.io/maturity-model/#knowledge-ratings-for-evaluation

Definition at K & S for "Optimize" is: (and also for other dimensions the word 'Full maturity' is used...)

Definition: Full organization ICT accessibility maturity. Organization-wide, role-based expertise in accessibility and disability inclusion is well-defined, evaluated, remediated, and continuously enhanced. Accessibility knowledge and skills are consistently implemented across the organization.

When "Full maturity" is reached, it seems like no need anymore for optimizing anything.
This should be changed to a state where you've reached Level 3 but there's always room for improvement.