With the monthly sub: the devs actually have the incentive to bring and keep new players into the game: the game itself has to actually be good. With microtransactional services they can not give a shit about the quality of the game itself and the number of players that want to play it; they can only care about old players making a pile of money for them; so they can feed into the addiction and sunk-cost fallacy of a few old players instead of making the game itself better that can bring actual people into the game as it used to be when mainly the sub made them money.