Copied straight from the rules post:
No discussing illegal activities - The internet is a big place. Take it somewhere we aren't responsible for. This includes piracy talk. Yarr!
Tekkit/Tecknic does not have permission from the mod authors to use in the modpack, so they are illegal and the rule says you can't talk about illegal things.
EDIT: Now looking at the title, Banned should be changed to Warned Then Banned.