Why not do the following:
- Get rid of Casual, have it be entry-fee only like arena
- Since it’s now strictly pay to play, make all cards “free” for deckbuilding (in reality you’re “renting” them like you do in arena)
Obviously all blizz cares about is monetization, and this would do that. There’s a lot of duels fans, and if they have to pay to play at least some of them will buy ticket packs to do so (same concept behind why arena exists), and by not requiring a collection (like arena), it makes the mode more accessible to people which would make it more popular as well.
Understandably, they don’t want to support a mode that doesn’t make them money, so just kill off the free version of the mode, not the whole thing.