About iCloud Mail

I would like to ask one question related to iCloud Mail. There are aliases (no more than 3) to hide the real Apple ID address from some online stores, for example. According to Apple's information, such aliases can not be used to enter iCloud. Previously, it definitely could not be done. Now I create a pseudonym and quietly enter my account at http://icloud.com or http://appleid.apple.com. Moreover, I even turn off or delete the alias of mail, but I still enter the account by a remote alias. Is it some kind of bug or Apple that included this feature? But then what's the point of the pseudonym ...