Another big motivation hurdle is wasted effort — I like to think up Weird Scenes Inside The Goldmine, but it's just a fact of life that nobody else really cares, and the chances are pretty good that the players will just ignore all that shit and go off and do something else entirely*. I'm not generally in favour of railroading an adventure, but it would be nice to be able to use my lovingly-imagined creations from time to time. It sometimes feels as though curiosity and adventurousness are an unwelcome intrusion into the game, rather than the underlying stimulus for the whole thing.
And another thing — I'm really not a big fan of constant city and/or detective and/or political and/or wilderness adventuring. It's fine as a leaven, but not all the time. I'm not good at acting and presenting NPC interactions, and all of those genres tend to require quite a lot of it.
I'm beginning to think that drawing a world map in the first place was a terrible idea. I should have just stayed with dungeons. In fact, I'm tempted to just send the whole campaign to Hell. Not metaphorically.
* The most recent example of that has come back and bitten the players in the arse though; if they hadn't ignored everything around them in their haste to go somewhere else, they would have found something that would have taken care of a certain problem that one of them has been whining about incessantly. Well, they missed it, so tough.