Why does the Pre-Order status shows "Stop selling policy"?

The "Continue selling when out of stock" option in the main Products page is untick.

When you see "Stop selling policy" status in the Pre-Order Manager > Product page:

That means that the "Continue selling when out of stock" option in the main Product page is untick:

This option must be tick to activate the Pre-Order feature.

 

Related Articles:

What does these pre-order statuses mean?

How do I enable/disable a product for Pre-Order?