Auto-closing of threads whose last response was over 12 months old is actually a plus.  All too frequently old issues with the sites/forums/software are 'revived' when they are no longer relevant....and thus redundant.  The poster is under the impression the issue is current without referencing/realizing their antiquity.
If a thread were considered historically significant Admins can reset/unlock them.
Spam-bots trawl for suitable 'phrases' on which to respond/post.  In fact one of Island Dog's long-since hidden was still being hit on a weekly basis.  Locking them cures that...