I think the biggest issue is that it is a collectible card game that isn't collectible. Hearthstone is constantly changing their cards retroactively. This means

I think the biggest issue is that it is a collectible card game that isn't collectible. Hearthstone is constantly changing their cards retroactively. This means the card you paid a bunch of money for can be retroactively changed into something that is worthless. In contrast, with a game like MTG, even banned cards can still retain a decent amount their value to collectors and casual players. You get what you pay for and it's yours forever to do with as you'd like. Why pay tons of money for ever-changing pieces of digital paper you don't even actually own?