Fame
Think about all of the famous principals you know, go ahead.
No, no, real ones. Not so easy, huh?
While definitely an important and necessary job, being a principal doesn't get you much in the way of national fame. There are a few select cases where principals do such a great job at improving a school that they make the news. Once in a while they even get a movie made about them starring Morgan Freeman. That's pretty much the dream.
You could also receive some recognition in academia, if you're a prolific writer or speaker on the side.
Even if you aren't famous to the general populace, you can at least be sure that your whole school knows your name. And truckloads of new kids are dropped off every year. They'll all be forced to watch you give morning announcements any weekday you want.
Gotta love a captive audience.