[thejeff]

It's not the time it takes to run the turns that bothers me, but the time it takes to play them.

Maneuver dozens of armies, rescript as necessary, try to figure out which battles were critical and what happened, what can I afford to summon, what gear do I need to forge for it, etc, etc.
You get so bogged down in the minutia, it's hard to remember what the larger plans were. You have to, and I like to, plan at least 4-5 turns ahead, but if it's going to be several days before I see how the plans going and how it needs to change, I've got little to hold my interest. I get to the point of, it's going to take another 10 turns or so to actually finish off the current enemy and I don't want to start another war till then, and lose interest.

MP is different, even when it takes as long, or longer. Since you can negotiate, useful planning can be done even longer term and there is far more reaction to what you do, so you can rarely just go through the motions with one strategy even against a weaker opponent.