The registar knows the person's email. But the DNS service often does not.
So the only way the DNS service can get a notification to the domain owner is if it's forwarded by the registar.
So the only way the DNS service can get a notification to the domain owner is if it's forwarded by the registar.
The DNS provider absolutely can send a notification to the registrant without having to 'go through' (meanining interact with) the registrar. Even a third-party privacy service merely exists as a notification broker. Any notification sent by the DNS provider would simply pass through onto the registrant directly.
[1] https://www.icann.org/resources/pages/governance/bylaws-en/#...