I agree, but to me, it is up to the OP to dredge up their own "dormant" posts, not responders.
And I also agree that older topics moved to Archives would be nice, but that would take a considerable amount of effort and time on the part of the staff. And these forums are managed by volunteers who are already contributing a lot of their own free time keeping it running smoothly and peacefully. Plus, in effect, when older posts are allowed get old, they become more or less archived as they drop down the list and off the page - unless dredged up again.
But more importantly, as threads are moved to different forums, links and redirects must be maintained, or broken and that makes database management much more complex, adds complexity to backups, and more.
And I agree people do go on vacation, get sick and even die. But I do note, in this case, the OP received two replies on the same day of his opening post, the same day he joined this site. And he came back at least once to edit his post. So unless he died, it appears he just decided not to return again.
So IMHO, if an OP has posted his problem and received helpful advice, but has allowed several weeks to pass with out returning, it is best to just let the thread remain dormant and fade away on its own.