Why does the lead time gap exists?

Supply chain managers rely on this time gap to allow them to prepare and deliver customer order on time.

It exists because it takes longer to procure, make and deliver the finished product to a customer than the time the customer is prepared to wait.

It exists so that the supply chain executives can rely on the more precise forecast$-$based rather than the less precise demand$-$based planning.

It serves as a measure of customer$$s order cycle time.