Why are privileges on KPI/Charts assigned in Role level not applying to Users?

Why are privileges on KPI/Charts assigned in Role level not applying to Users?

If there are certain privileges assigned under a ROLE then, all the privileges assigned for a ROLE will be inherited by the USER under that ROLE, if there is no specific privileges assigned at the USER level. However, if there is anything specific assigned at the USER level then, the privileges assigned at the USER level will over ride that of the ROLE level. Therefore, the existing individual USERS under the ROLE might have privileges assigned at their individual USER levels and hence it is not inheriting from the ROLE level. However if a new USER assigned under the ROLE, it will inherit privileges of the ROLE.