Why do we need Purchasing attribute fields to release planned orders when internally transferable.

We have business case as below:

• Package Version Items: These items are not intended for purchase from external vendors; however, they can be transferred between organizations. When the forecast is prepared based on previous transfer order shipments, these items appear in the supply plan with a release status of 'Ineligible' and the error message: "Order cannot be marked for release as a purchase order because the item is not purchasable."
• Items Restricted to Central Warehouse Purchase: Certain items are intended to be purchased only from a central warehouse, with material transferred to other warehouse locations as needed. Since purchasing attributes are not enabled at the destination locations, the supply plan associated with these destination organizations marks the items with a release status of 'Ineligible,' accompanied by the error message: "Order cannot be marked for release as a purchase order because the item is not purchasable."