Maybe Blizz are bummed that Valve have turned Dota into a huge thing. The current TI prize pool is @ $12,610,645, and Valve are basically drowning in money now, so Blizz are trying to eat into CSGOs market?
http://dota2.prizetrac.kr/international2016
75% of all store purchases go to Valve... and the rest to the prize pool, if the prize pool (from sales) is at 11m... doesn't take much to figure out how much Valve are getting :O