As per Tableau site
Add the Tableau users or groups you want to receive the subscription. To receive a subscription, users must have permissions to view the content. If they use Tableau Server, their accounts must also have email addresses.
It's a bug if happening .
Hi Ritesh - it seems then, that you agree that if a user no longer has permission to a view, they should have their existing subscription unsubscribed/removed? I am certain other folks must be running into this?