Expanding on what Colibri said:
In some forums, such as the Pit, we really do NOT want zombie threads. There are two main reasons:
(a) Some of the people who posted to the thread two years ago are no longer posting here, and can’t defend themselves or respond; and
(b) There are issues that have died and time has healed over the wounds, and we don’t see any point to some newbie unwittingly picking at old scabs.
This is less an issue in (say) Cafe Society, as long as the new posters understand that the posters from two years ago may not be here, may not be reading that thread, etc. and many not engage in discussion. There’s less “attack” mode in Cafe Society than in the Pit --someone not being able to defend their position about some TV show is different from someone not being able to defend their character against attack.
Thus, in Cafe Society, CCC, CSR, and GQ, it’s OK to add thoughts to an old thread. In the Pit it’s absolutely not OK. And in MPSIMS and IMHO, it’s generally not OK.
In general, resurrected threads are at least a minor nuisance in any case. To make the point by using an example: You see someone complaining that their landlord searched their apartment while they were at work and stole money (say.) You get indignant on that person’s behalf. You read through the thread, really building up empathy for the person, and then, two pages later, you discover the incident happened four years ago. Some newcomer just put “That sucks” at the bottom. So, you’ve got all worked up over some issue that’s long dead. That’s annoying. Worse, sometimes, you don’t notice that the thread was old, and you try to interact with the prior posters, giving sage advice and well-thought out comments, and then finding out your efforts were completely irrelevant.
The topics where this is most annoying tends to be those of the Pit, IMHO, and MPSIMS. Topics in CoCC, Cafe Society, GQ… well, it tends not to matter so much if you see a thread about a movie that’s four years old, it’s still around on DVD. It doesn’t matter too much if you have comments on Cecil columns, or have further information about some GQ question about Christopher Columbus.
That’s why, in some forums we care and in other forums we don’t.