Why Can't the National Constitution Center Keep a CEO?

The Philadelphia Business Journal reported that National Constitution Center CEO David Eisner is resigning after three years on the job. That's news, of course, but here's the line that really sticks out (emphasis mine):

Eisner is the center’s third CEO since it opened at a cost of $137 million in July 2003...

Wouldn't one think that if you're passion lies in running an exhibit or museum focusing on history that being CEO of the National Constitution Center would be a destination position, not a transition position? Shouldn't we expect to attract a high profile star to this spot and, likewise, expect them to make this a place to make their name?

Bottom line is, that's a lot of turnover.