1. If necroposting isn't allowed to prevent spamming why aren't very old threads lock?
From my perspective of view, there are boards and threads which are self moderated and locking of such threads can only be done by the OP on the other hand most times threads are locked when it seems spamming is getting so much on it even after an answer or a solution has been provided to those threads.
There are threads that even without locking them, it seems that it has already been exhausted and more newer ones tens to push to those down.
2. If I come across an old thread from 2021 and I think I have new input to contribute, would do you advice me to start a new thread instead of bumping the old one?
Yeah, it will be better you start a new thread and make some reference to the previous thread rather than going to kick start a discussion you weren't there from the start