Why WoW makes for such a great Hobby game

Sticking with the conversation from my earlier post about the different types of game players, I wanted to speak specifically to why it's so easy to be a gamer hobbyist in WoW.  The first and foremost factor is the challenge of the game.  It's really hard to play games as a hobby when the game is easily beaten and I'm thinking specifically of console games like Call of Duty and the like.  You can only run a map and PvP for so long before all luster is lost.  The Warcraft world, specifically the actual size of the world is large enough to occupy your attention for months on end.  For instance, if you wanted to simply explore the planet of Azeroth, it isn't something you can do in a matter of hours, days or even weeks.  If you are going to explore Azeroth, you are looking at a commitment greater than just entertaining yourself, you want this for other reasons.  However, the reason we do things as a hobbyist vary widely however the one similarity that all hobbyist share is that they are willing to commit.

I keep falling back on the example of  hobbyists who build wildly complex and surprisingly accurate ship models inside bottles.  I'm sure this particular hobby has fallen out of style, many who are under 20 probably don't know what I'm talking about (google it, it's mind blowing what people make) but take a second to itemize what kind of skills and patience you would need to make such a thing.  It's probably not overly difficult, but people who are passionate about it, are willing to spend the time.  This is the case with WoW, it's a game designed for all ages, including the very young, but it doesn't patronize it's older players with content that isn't stimulating.  The game requires that you do certain things to progress in the game experience, but it offers so many options to what you do, and how you do it, that it seems to me that the possibilities are endless.  Endless enough that one could play for years and not be able to claim to have done everything the game has to offer.  This simple reason is why the MMO and WoW specifically are so conducive to hobbyist play. 

What are some of your reasons for playing games?  If you are a hobbyist, what are some of your reasons for being a gamer hobbyist?