no idea

ask some more

A quick forum search might give you a clue. You can seach by using the withe box on the top right corner.

sue them

everyone gets spammed with dota2 and if we were allowed to create giveaways, there would be thousands of pages of dota2 and the site will probably die.
not to mention it's a beta the should be become f2p soon.

go on wall of shame

There are 25,352+ reasons why you can not giveaway Dota2 here
They can all be found here http://steamcommunity.com/id/dota2bot

It's been permanently removed from the list of giveaways, because it was exploited. There is your answer, now off to the Wall of Shame with you!!