Here's why I believe it's failing.
I've seen it a few times in here already, but in almost every Artifact thread, people post that video of the crowd reacting to the announcement of Artifact in TI7 and say that's the reason it flopped. That's not the reason.
They say it's because "no one asked for it", that's also not the reason.
The two biggest factors were the buy-in cost and the messaging of how the game modes actually work.
1. Buy-in cost
Buying in for $20 gets you the basic cards, and 5 card packs. This is enough to easily build a deck in Constructed, but it may not be the deck you want. However the problem with this was at launch, the only way to get more cards was to either buy packs, or play one of the Prize Play modes. Lots of people thought it was kind of bullshit that you were paying to pay more money. That's not completely true, but I'll cover that in the second point.
2. Messaging on how the game modes actually work
There's a grand misconception that the only way to play matchmaking is to play Prize Play, which costs a ticket to enter every time. Tickets can be bought, and they can be earned from the newly-added progression system, and won back from Prize Play. However Prize Play is only one section of play modes. There is the Standard Play tab, which includes the following:
A Constructed matchmaking mode, just puts you in a single Constructed match
Constructed Gauntlet - A gauntlet like the others, but with a constructed desk. Try to win 5 before you lose two.
Phantom Draft Gauntlet - Same as above, except it's Phantom Draft, which is a pretty good mode. You draft for cards, and then build a deck out of the cards you draft. You also have access to the basic heroes and can have duplicates of a hero in your deck (up to 3 of a hero), but all other limitations apply (no more than 3 of a single card, with the exception of signature cards if you have duplicates of a hero).
These free modes are the best to play in my opinion. Being able to win more cards in Prize Play is nice, but I am perfectly content playing free modes.
3. It's not clear how much the cards actually cost.
Pack costs are very clear and up front, however what about getting the cards you want? People can often compare them to Hearthstone and other digital CCGs. However, in that aspect, Artifact is THE CHEAPEST. You need a specific card? You can go on market and get that card. Most of the cards cost mere cents, with some of the rares approaching $1-2. It's cheaper than Hearthstone, where you have to buy packs, and dust enough cards to make the cards you want if you weren't lucky enough to get them in packs.
I think Artifact's issues were all in it's messaging, not the gameplay. The thing about it being a complicated game is a non-issue IMO. There are plenty of complicated games out there that people have zero problem playing. LoL and Dota are both very popular games, and pretty complicated, especially Dota. Dark Souls is extremely popular and it can be complicated to play the game well. It goes just beyond rolling and shielding...but with stuff like getting the right stats, and optimizing your equipment so you can actually roll decently, dealing with the PvP aspects, etc.
