As others have pointed, it is not a direct cause but pretty much social trend. Both Wii and WoW plus the gazilions facebook games and mobile games pretty much a catalyst of the big changes in gaming landscape. The popular trend is now all about casual gaming, creating games that is easy and fun to play, and yet strangely addictive. Not to say that hardcore is dead since plenty of games are still hardcore to the bone, ex: Demon Souls, Dark Souls, Tactics Ogre, Starcraft, etc... But overall the floodgate to the untapped casual market has been wide opened with the Wii and WoW - hence the shift with FFXI, and the big fat failure of FF14, gotta evolve if they want to survive.
Also if you look at the recent FF games, all of them are embracing the casual aspects. Personally it is great that FFXI is becoming more casual friendly, gaming should be a fun activities and not "achievement" by grinding and wasting tons of hours farming and camping - but to each is their own. I am not saying that FFXI should clone WoW but they certainly can take inspiration from many other Japanese games like Monster Hunter, Pokemon, Final Fantasy Tactics, Persona, Tactics Ogre and Phantasy Star Online which are addictive, fun, and still able to maintain the hardcore aspect of the game without watering it down so much.