This also has the side effect of making your email list have better deliverability. If you consistently have good open rates, Gmail and other email providers tend to mark your content as spam less often.
Mailchimp recommends [1] pruning out inactive or "low star" members semi-regularly for this reason.
Aha! Makes sense. Especially if these publishers offer email marketing as a service to other publishers.
I remember hearing that before long ago but it slipped my mind. Thanks.