Many, many questions have good answers, ignored or forgotten by the OP. A significant part of the issue comes from users unfamiliar with the site and the basics of accepting an answer.
Could MSE send an email to each user with unaccepted answers? The friendly email would contain links to eligible questions as well as simple instructions on selecting an answer.
This is a win for the OP as well as those who crafted answers.
This is in the vein of “Welcome to MSE…”: Popup to remind new users to upvote and accept answers.