How do unengaged recipients hurt delivery?

In the comments Ulrik asks: “How can unengaged recipients hurt delivery if they aren’t complaining? What feedback mechanism is there to hurt the the delivery rate besides that?”
There are a number of things that ISPs are monitoring besides complaint rates, although they are being cautious about revealing what and how they are measuring things. I expect that ISPs are measuring things like:

• How many users read a particular mail?
• How many users click through on a particular mail?
• How many users have the senders from: address in their address book?
• How many users receiving the mail have abandoned their accounts or not logged in for months?
• How many users never open a particular mail?

Some of these values senders can measure as well. Senders know, for instance, how many users click through on a mail. They know that some people do open the mail, and they know that some people don’t open the mail. The numbers on opens are not always completely accurate, as to measure opens the recipient must load HTML images. But images are not rendered by default in a number of email clients, and some ISPs don’t show images unless the recipient agrees, or the sender is in the recipient’s address book or the sender is certified by a 3rd party.
Senders don’t have any way of knowing, however, if an email account has been abandoned. That’s something that only the ISPs know. Because of the tools that senders have, there is no difference between an account that doesn’t load images and doesn’t click on any links and one that has been abandoned. Both of these cases will hurt a sender’s reputation, but the abandoned account will hurt more. The ISP figures that if you’re sending mail for months and months to recipients who don’t even log in, that you’re not engaging readers and sending mail recipients want.
What can senders do?

• Senders with websites requiring a login can disable email to that user. The users account can be  and notify users that they will need to resubscribe to the email list when the user next logs in at the site.
• Senders that do not have registration can send re-engagement campaigns to recipients who have not clicked or opened a mail. Users that do not interact with the mail are dropped from the list.

Yes, you will lose names off your list. But those are people who aren’t interested enough in your mail to read it or click on anything for months and months. What value is that name bringing to your business? Does that value outweigh the reputation hit that continuing to mail non-responsive addresses brings?