Loot Boxes have existed for over a decade in games like ZT Online and Lord of the Rings: Online... The first AAA non-online, non-free game to have Loot Boxes was actually Mass Effect 3 in 2012 which was then followed up by Counter Strike Global Offensive.
Blizzard is NOT to blame for this, they just jumped on an already moving bandwagon.
Though, they do deserve the criticism they get considering it was a AAA game with no singleplayer, minimal amount of maps and game modes, so it wasn't exactly content rich to justify the price tag to begin with. (Heck, it still isn't content rich.)
With that... We could actually place the blame at Bethesda's feet with Oblivion thanks to Horse Armor, which proved to all developers that placing a price tag on even mundane pieces of digital content can turn allot of money, which in my opinion is when the beginning of the end started.
In short though... People keep paying for Microtransactions, DLC and Loot Boxes... Companies are out to turn a profit, if people keep buying them, then companies will keep providing them, it is the consumers onus to take responsibility and say "no" and vote with their wallets if they truly wish to put a stop to all this rubbish.
--::{PC Gaming Master Race}::--