This Dealer disabled the customer portal because they did not want their customers to have the ability to request service from the portal. They did want them to have the ability to pay invoices and add payment methods to their account. Follow these steps below to disable work orders from the customer portal
1) Click on the Setup and then click Preferences (under the User Manager Table)
2) Click on the Customer Portal tab, uncheck the Enable Work Orders checkbox and then click Save
3) Doing so removes the Work Orders tab from the customer portal altogether so the end user will not be able to request service from the customer portal