To me, when i start a new game, i grind because i want to:
1. explore the environment
2. find the goodies (weapons, gears, whatnot)
3. see what's to challenge (monsters, quests)
4. get the next spells, powers, skills, or whatever you get when you level up
I gotta say that i don't go 24/7 but i do grind some days.
Oh and when i think i've seen enough, I hope on the next train to the next game. Like i did with all the mmos i've played: UO, EQ, FFXI, WoW, FlyFF, and now the new flavor is Fiesta

Now that's on a good 10 year span.