Good question. (By the way you can send me your questions at jmayhew / ku / edu.)
Part of the problem is that gratification is so much delayed in this insane profession. Monetarily it involves years of working at very low salary. Eventually you might make some half way decent money--or not. A review might appear 3 years after publication of the book, and thus 6 or 10 years after you first had that brilliant idea. The work itself is gratifying, though difficult and rather solitary. In many departments (though thankfully not in mine) the colleagues are insufferable and the infighting fierce. The people most in position to judge and appreciate your work are few in numbers, geographically scattered, and might be your rivals. Even other researchers in the humanities often act as though research in the humanities were pretty much worthless, so don't expect the general society to hold it in high esteem. It's seen as something we do for ego gratification.
The main reward, then, is getting to keep the job that lets you continue to do it. We need motivation in order to keep going in the short term, where any kind of extrinsic rewards are nebulous and delayed. The attraction of blogging is that it allows people to read what I write minutes after I write it, and possibly respond or comment. I really need that day-to-day stimulus.