Why does Microsoft make it impossible to change ownership of an Xbox account?

My kids were too young to have their own accounts on the Xbox, now they are teenagers and have spent alot of money and earned a bunch of achievements, but Microsoft says I can't transfer the account to their email because it's tied to mine. Don't act like it's difficult to do, it's a single database update command. I don't want to create an alias on my account, they need their own accounts. This is just shady business by Microsoft trying to control who owns digital property.

:)