The online Help section within the Adding and Customizing Unsubscribe Links page mentions Detail Products and Detail Groups restricted to the recipient do not display in this list:
How is this configured?
If users want to restrict products from appearing on the unsubscribe page, populate the field Restricted_Products_vod of the corresponding Account with the restricted product name. The product is not displayed in the product list on the unsubscribe page.
CRM Related Documentation: Restricting Products by Account