How is that a good deal for the public, we promise to uphold a perpetual copyright and in return we get ...? Copyright is a deal, we uphold a legal defence for the author [or their successor] to monopoly rights on their work and they promise to put the work in the public domain when the term expires.

The public domain release is the payment to society in exchange for the monopoly rights protection.

Why would the public go for the deal that you suggest?