Why variant has to have default UOM same as that of Template

When I change the default UOM of a variant say from KG to meter, while the default UOM of Template (from which the variant is derived) is KG, I see a pop-up on saving that
Default Unit of Measure for Variant must be same as in Template.

which is clearly in-line with code at erpnext/item.py at 4055cc76a73037fce8afe74a1aadbb4b3e16f6a9 · frappe/erpnext · GitHub

But what is the reason for this restriction?

Tagging for reach.
@rmehta @revant_one @peterg

In v13 it is even more frustrating. There is this bug, where if you create a new variant (+item -> wizard -> check varant) it sets the default UOM to tos. Which means the wizard fails.

What works is to go into the variant and then at the top there will be buttons where you can create the variant that way. This works. It generates the correct UOM based on the variant template.