Personaly, I lose any motivation to play an RPG if there isn't a story or some quests that are more than filler content. Exploration elements and character development might keep me busy on their own for sometime, but after a while, it's bound to get boring. Especially since the gameworld simply can't keep reacting to my character's development forever. Why waste all that time on some virtual shit world with nothing emotional to keep me hooked? I'd rather spend that time on exploring the real world locations within my reach, or do anything else useful.
Quests need to be more complex perhaps, to support ever-growing gameplay and character options. If MMORPGs were done right in the first place, ie. players forming factions, forming stories and lores of their own, it might be an interesting option to waste such time on them. Alas, MMORPGs are moron magnets.