Why is UOM required when selecting All Items

Summary:

In Channel, for Product Rules, when I am selecting All Item, UOM is mandatory. Why? What is the behavior of this set up when we have AR Transactions with Items with different UOM?

My client requirement is to be able to configure Product Rules for all items which may have different UOM . When I am running Create Accruals for Channel Batch, it does not pick up this Customer Promotion Program. I was hoping for this use case UOM will not required.

Am I using the correct Program Type? Please advise.

Program Type: Customer Promotion

Product Rules: All Items

As you can see if I am selecting UOM, and AR transactions for this Customer A will have items with different UOMs, will the Create Accruals for Channel Batch ESS job pick up this Program to create accruals?