Why was my PO not created automatically?

For POs1 Purchase Orders to be created automatically from Customer Order, you need to ensure.

Available stock of the item in the warehouse is not enough,

The item must not be of type Manufactured Item,2 If it's of type Manufacturing Order, a Manufacturing Order will be created instead of a PO.

The item must have a designated supplier specified in the item master, and

The back order type for the order line must be Order Now.3 This is defaulted from Customer Master.