You've never been involved in any form of activism, I take it? It's no cult; people who want to work for a political campaign are activists like any other. They are devoted to a cause they believe in, and will happily make personal sacrifices to strengthen that cause.
The activist spirit is alive and well in campaign employees.
Maybe you've volunteered for a charity? Volunteerism is the other half of the equation. Campaign employees are part activist, part "paid volunteer". Anyone who's volunteered for their kids' school, for a neighborhood charity, or for some other cause knows the positive, almost euphoric feeling that comes from volunteering for something that is meaningful to you.
In a time where most of us go to sleep feeling existential dread because we can't do anything to stop the various runaway trains we see in our society/planet/etc, volunteering can provide a feeling that you're actually doing something to make a difference.
That spirit, too, is alive and well in campaign employees.