Before someone corrects me, let me already point some things...

Hearthstone has multiple Blizzard-sanctioned tournaments during the year, some like the last Blizzcon tournament alone had a 1 million prize pool. Some HCTs had 250k prizes, others 100k. Mind you, there are lots of HCTs every year.

The 10 million prize pool from Magic is across multiple events, both online and tabletop. It's not a single show like the International or Worlds.

Magic investment may look big but when you think how it's distributed it's not that lavish and I believe Blizzard may be spending even more on Hearthstone. However, I feel every company is trying to show they are the be$t e-sports out there.

However, the headline of 10 MILLION PRIZE surely looked nice and it's not like the other companies don't use similar methods.