I think instead of locking threads Moderators and such should be able to delete the thread and then post a comment on the thread creators profile telling them why it was deleted. Otherwise all the locked threads just sit there on the forum pages wasting space.
Moderators lock the thread only to preserve the AP users gained by posting there. If we deleted every locked thread, for whatever the reason, users would lose all the AP gained in said thread. In most cases, those posting wouldn't even be part of the problem, save for a few or one single instigator. Moderators will only delete threads for stronger reasons, like blatant violations of the T&C or excessive spam in the entirety of the thread.
For the second part, users are always welcome to ask the moderator why their thread was locked, moved, or deleted. We tend to help by adding tags next to threads, such as [ans] for "answered" and [req] for "request".
That's a horrible idea. If the thread is completely against the rules, then yes, it should be deleted. However, if it's a good thread but someone decided to derail it, it's answered, requested lock, etc., then it should only be locked. People would lose thousands upon thousands of posts if all the threads were to be deleted, and many people wouldn't be pleased with that. Also, if you were to delete all locked threads, then some stickies would be deleted as well. Those are there for general information/they are important threads. I don't see how they are wasting space. Just because they are locked doesn't mean they are wasting space. And Armor Games doesn't have a "thread limit" so there's no use in deleting threads for this reason and the ones already stated.
In some cases we also leave the thread in the forums so anyone with a similar question have a chance of finding the answer in the forum and so the creator of the thread can see what everyone replied to them. Rather than, say, copy/paste every single post in the thread to their profile.
Locked threads aren't necessarily bad or trash or something. They are just not open for posting in any more. That doesn't make the posts in them invalid.
Moderators and such should be able to delete the thread and then post a comment on the thread creators profile telling them why it was deleted.
This specific thing is something we are able to do, btw. I've done so a good handful of times in the past. We just don't do it instead of locking.