Imagine if WoW classic has the playerbase of City of Heroes, Age of Conan, Diablo 2, or the original Starcraft series (outside of Korea) 5 years from now?
Would you REALLY call that successful, to have over 100x less players than it does today? A 99% player drop off rate?
Not to mention- those games still receive fixes and updates occasionally (such as Starcraft Remastered)