Can the mods not lock the threads...? Not that I do, but if I wanted to post on an old thread - I would... That's the nature of forums.
Mods lock them or it will keep happening... :/
Why should it be locked, if the thread doesn't break the rules? There are tons of discussions that started in 2012 and have been active since. New threads get started to discuss older events. Although some responses might be outdated, I don't see any major reason why old threads should be an exception and get locked just because a user hasn't posted in said thread for X amount of days/months/years.
I'm not the one moaning... Perhaps people should just "deal with it" then...
I believe the OP's main concern was that some users maliciously attempt to pad their post count with posts like "I agree" or "This is scam", when the website has closed down. In such case, I'd suggest reporting any posts whose main intentione was to increase the amount of posts made.