How to delete an old yandex account by phone number?

Question

Yandex

If you register a new account on yandex without a phone number, you can only delete it using a security question, but if you add a mobile phone to your account, you can delete it by receiving a one-time code in SMS.
For old accounts, adding a number does not change the way the account is deleted, they also ask for a security question.
Is this some kind of Yandex glitch or some artificial discriminatory restrictions for old users?