Because it's the forum rules, that's why. Go give them a read and you will see it.
That's what Ghaz said... if that's considered arrogant and unhelpful then you've got REALLY thin skin...
Automatically Appended Next Post: http://www.dakkadakka.com/core/forum_rules.jsp
Linky to the rules in case you need them... which I'm sure you don't... but I'm being helpful!