Gamers of the new generation generally* don't match up with the characteristics of old MMORPGs (the "Korean grindcore" types). They no longer have the ability or desire to devote a lot of their time to a single game and are much less willing to repeat boring tasks at the prospect of rewards. They want pretty much instant gratification and gameplay without much hassle and waiting.
So while the kind of MMO's you saw 10-15 years ago are a dying breed (in the West at least), the "Age of MMOs" definitely hasn't ended yet. MMOs have simply evolved to be more suitable with the new generation of gamers.
* Note: generally. As in, a generalization. There may be outliers. Don't bother responding something like "hey ur theory is flawed cause im from this generation and i still love doing this and that"