The theory I’ve always heard about why the shuffler might be biased is that they’re trying to reduce land flood/screw. Drawing too few or too many lands is a commonly cited cause of frustration with players and if you’re reasonably assuming Arena wants to do all the usual monetised-game things of increasing playtime and MAU whatnot, this conclusion seems one of the first people come to.

They make money by selling the cards right? I would think that might change their incentives somewhat. I don’t really know the game.

The better "experience" they transmit to the players, the more engaged they will be and the more cards/packs they will sell

Players who aren’t having fun won’t buy cards or will stop buying cards when they quit.

Yes, but a frustrated player is more likely to buy event entries, aka gems, to draft more, and blame the poor randomization on bad luck, rather than intentional screw, because that is what you do at real life events. It's an insidious dopamine loop strategy, but it absolutely works.