It is quite often seen as an attack on the other thread or people on it and so I suppose comes under the 'no personal attack' rule, which makes sense - actually starting a whole other thread to bitch/complain/tear apart a poster or posting is a fairly big attack.
If you have a view on the topic, or a problem with someone on the thread - take it up with them, don't go start another thread and try to get some sympathy/support. It's cowardly and a bit dim, since everyone can still see it 
If it's made you think of a similar issue, or related issue, or just made you think of something seemingly unrelated - then it's a separate thread and there's no need at all to link it to the other one.
(general you, not you you)
Often threads are started about deleted threads. Well, if the first one went, then one starting it all up again is just going to go too
I am surprised it is not in the Talk Guidelines. If it's not against the stated rules of the forum, then they shouldn't be deleting them, should they? 