Why do projects check budget by PO line level instead of PO level?

Summary:

Why do projects check budget by PO line level instead of PO level?

Content (please ensure you mask any confidential information):

We use project budget for PR and PO. We will also transfer multiple PR lines into one PO. But the system will limit each PO line amount less than or equal to PR line amount.

It’s not reasonable. It should check the project budget by the whole PO not a PO line.

Now the budget check logic:

It should be total PO line amount must <= total PR line amount 100

Version (include the version you are using, if applicable):