If the wider audience base didn’t buy cards and still play the game they wouldn’t continue to power creep. Clearly it does sell as their quarterly earnings have shown. They also need to compete with Snap, which aggressively monetizes and pulls in large numbers through flashy power cards as well.
Changing things in game is much harder for HS though. They have already said the games base code limits them greatly. I wouldn’t want to look into that code on my best day. It’s probably a fragmented mess. If they had the resources they should rebuild the engine from the base up but they don’t.