About the Purchases Subpanel in Product

I think it is deliberate:

SuiteCRM/modules/AOS_Products/AOS_Products.php at master · salesagility/SuiteCRM · GitHub

It is basically a list of Quotes related to the Product.

I understand why you would prefer your logic, it also makes sense.

May be with some custom code you can make a new subpanel for what you want (are you a developer?):