> I've never once been automatically unsubscribed from anything.

To be fair, this is the kind of thing where, if it had happened, it’s possible you wouldn’t have ever noticed.

Hi, pleased to meet you. Even though everyone on our newsletter list specifically signed up to get newsletters, we’ll still warn you and then unsubscribe you if you do not engage for a long time.

Google, in particular, will send all a sender’s mail to everyone’s spam folder if it sees low engagement across all gmail users... so it is in publisher’s own self interest to remove disengaged users.

I believe mailchimp has something that automatically unsubscribes users if they haven't opened your emails for x time, but the amount of publishers that use this is probably pretty low.