They are greedy that milk people with addiction problems and sunk-cost fallacies. They already make a mountain of money from microtransactions so the monthly fee is a cherry on top at this point.
I personally find the subs per month to be 1,000 times better than microtransations and I wish it was still only that; now they don't give a shit if the game has new subscribers; they can milk old players with addiction issues.