As someone in their exact target demographic - I play Magic Arena and Hearthstone regularly - I think they messed up the business model. I don’t mind paying $50 for a game or $20 for an expansion, but I hate getting nickeled and dimed and I was put off by the fact that if I ended up really enjoying the game there wasn’t a path to continue playing without continuing to pay every time. Felt like gambling not relaxing.

Valve has never been good at building progression systems, and that's exactly what killed Artifact.

You get no rewards for playing the game. If you want new cards, you have to spend money on packs or spend money to enter drafts.

This old fashioned "just play the game because it's fun" mentality is dogma to Valve, but nowadays users want and require the Pavlovian reward systems.

It had an upfront cost (where all the competing card games are F2P) and a cost to play as well as to acquire cards, which put a lot of people off. It is also a more complex game than say Hearthstone, but I think the success of MOBAs proves that complexity is not an inherent barrier to popularity.