The main reason threads close after an extended period of inactivity (30 days with no new activity is the threshold) is to prevent the inevitable thread drift. Generally threads that never close eventually cease to have any real relevance to the original topic and as a result oldtimers tend to start tuning out new posts to such antiquated threads almost entirely, resulting in predominantly only new visitors posting to those oldthreads and wondering why all the established members seem to be ignoring them (some taking such quite personally). In addition, this is meant to be a more informal forum and there is neither a penalty nor a curfuffle on this forum if a new visitors happens to ask a question that has been covered 20 times before over the past 13 years because they were unable to locate all those old threads from many years back. Well, that and the fact that almost nobody will ever take the time to wade through threads that are many dozens, or even hundreds, of screens deep...particularly given the usual topic drift associated with such long running threads, so at that point what function do those threads really serve any more? They'll get us lots of extra Google hits, for sure, but there is seldom much useful content that the visitor can still locate in such threads after they click on the search link and try wading through it all.
With sites that never close threads it can be especially difficult to locate relevant answers where the content they are really looking for is likely buried miles deep in threads hundreds of screens deep that technically had nothing to do with the original topic the visitor was searching for -- it is difficult to know you need to search a thread on "
tablesaw blades" to find the tip you needed on "
spray finishing"! Anyone who has ever researched a Windows related issue has no doubt numerous times stumbled upon a such forums where an old Windows 2000 thread, now more than 1000 screens deep, and 18 years old, is still being actively posted too -- yet almost all of the content in the thread has little, if anything, to do with Windows 2000 nor the original issue with that operating system that the thread purports to cover, rather people have continued to post thousands upon thousands of random Windows 98, ME, XP, Server 20xx, Vista, 7, 8, 8.1, and today they will still be posting Windows 10 questions to that same ancient thread...and likely some Linux and Mac OS questions as well, just to round out the topic drift And, of course, no thread has truly reached driftopia until the Nazis, Hitler, and Nuclear Armageddon are somehow brought into discussion through grammatical and topical gymnastics worthy of the next Olympics! You see, it just happened in this thread, too.
But ultimately it makes for a more topically relevant site since most threads never drift too far off their intended topic and the various topical forums we have actually retain a far higher degree of topical relevance which makes it much easier to search on your intended topic as the answer is highly likely to appear within its logical forum section. It also helps to keep things friendly since even more heated or controversial topics will eventually come to a close which greatly reduces the need to moderate member posts or behavior since someone stumbling on the thread months, or years, later can no longer bump it to the top and reignite the conflagration all over again...and again...and again....
That said, the original author of a thread may
always request that an admin reopen a closed thread of theirs if they have need to continue a past thread that has been inactive for several months, such as if following up on a tool repair where it took months to obtain the parts or to find the shop time to effect the repair.
