Because your system was designed to receive routine PM's. Its uptime reliability will be directly affected by the frequency and quality of your PM.
Your practice and patients are depending on the safety and protection it provides. Practices that do not maintain required safety standards open themselves up to potential lawsuits.
Accreditation and insurance companies require the equipment to be maintained to manufacturer's specifications.
Internal and external cleaning of equipment (required for system operation, cooling, and maximum system uptime.)
Verification of proper operation (includes phantom pictures which document system accuracy, penetration, and clarity.)
Electrical safety (verification of system leakage current and safety standards required by law.)