Considering we don't live in a vacuum, it probably was a combination of everything that everyone is saying. Some bad timing due to MtG Arena, scary gameplay which is hard for new-ish players, and a pricing which wasn't terrible but wasn't appealing either. Combine that with not releasing with any form of progression and then when they finally added progression it really wasn't much. Also, the major negative publicity around the pricing probably hurt it as well, some reasonable and some uninformed. Though as 2 or 3 weeks ago you could own the whole set for less than $100 dollars.
I still love the gameplay, but I don't play any game that has no progression or half-baked progression for long.
I hope they release one more set along side a big feature patch to give it one last shot. Something with actual ranked progression, cosmetic rewards, observer functions, and maybe a change to ranked pricing but as of now, similar to HS, people can go infinite in ranked draft, so I have no idea what that change would be.