Where does dota 2 prizepool came?

If you haven't yet heard the news, well it's still not too late to join or build a team to compete to Dota 2 Tournament because the The International 2016 (TI6) Current Prize Pool in Dota 2 is $18,389,342.00. Yeah you got it right, freaking big, I think its time to change my career and use my latent talent in Dota now.

Compare to other competitive esports game this past year that i've mention in my previous post, it is the 2nd biggest but this current prize pool will still continue to rise not not yet final.

The question now is "Where does dota 2 prizepool came?" or "Why is dota 2 prizepool so big?". For those of you who does not know Dota 2, let me enlighten you with some wiki:

"Dota 2 is a free-to-play multiplayer online battle arena (MOBA) video game developed and published by Valve Corporation"

 -Wikipedia

Well even it is a free-to-play game on steam, Dota 2 has a huge market where they sell items ranging from Hero Sets, Terrain effect, Weather effect, Game Announcer and many more.

And every year before a tournament is about to start , they add an item called "Compendium". This item contains alot of unique things that extremely awesome that is why this is so attractive to buy (dont as me if i have all of compedium). When players pay money to buy this items,  not all the money is sent to valve( Dota 2 company) , its like 25% or 50% is added to the prize pool of the tournament and this is why Dota 2 prizepool is so big. I think this technique also help boost the community to play and buy more item. We can say that more player in dota equals more prizepool "Crowd-Funding"

But do not be afraid, this so called paid-item main purpose is for pure cosmetic only nothing-less nothing-more, even though its freaking awesome to have immortal or arcana item.