Please feel free to tell me where it says that.
Quote from the Rules Thread:
"A Note on Thread Necromancy
We've been getting quite a lot of reports lately of people "necroing" old, threads, this is not actually against the forums rules.
The only time you need to report a necro is if it's particularly low effort (Responding to a thread that's long long dead with nothing but "Me too" or, "help pls" etc) since that actually violates a rule.
Understand that it is a faux pas to resurrect a very dead thread without good reason however and mods reserve the right to punish for lack of good sense."