On pre-orders: why do I see it always said that shopify can't accept pre-orders without another app?

[iltl32]

If I were to create a product called Item 1 - Pre-Order, and put in the description that it is a pre-order that will ship in X months, and check the box for "continue selling when out of stock", people could place orders for this item even when it's sold out.  I'm not using automatic fulfillment or anything like that.  Why couldn't that be used to take pre-orders?  Is there something in Shopify's system that would eventually kick the order back if it wasn't fulfilled for X months or what?  I don't understand the difference between this and using an app.  Please let me know.

Thanks!