Because you are ruining the game for other people, and that is against the rules. Every single time you log into the game you accept the
Terms of Use. Under chapter 8 section c) it is stated that:
You were breaking this rule by dragging mobs to them and getting them killed (on purpose or by mistake, it's irrelevant).
This has nothing to do with "free" skilling, or depo vs non depo. The only problem you have, and the only reason why the official punished you is because you are, literally, interfering with other players hability to enjoy the game.
Stop playing victim, stick to the rules and nobody will bother you.