It is explained in the article:
"At the same time, we have a duty to protect the Arm brand, which has been built over more than 30 years. Like all companies with registered trademarks, Arm is legally obligated to ensure those trademarks are protected and used appropriately. We recognize that this activity is sometimes met with frustration and are actively working to find a solution that works for all parties involved."
It's not about 'rules', it is a legal requirement.