I do adjunct, not for the money, but because I enjoy it. I do get paid a premium over certain other adjuncts, for teaching in the business school. I also used to teach in tech at another school, and got a premium there as well. I'd been told the premium was to entice people in the field to teach, as there's more demand for adjuncts in certain of these fields then there are people with the skills who are willing to teach.
My husband actually adjuncts with only a bachelors degree, because so few people have the skills required to teach the class he teaches. And yet we know tons of liberal arts PhDs who can't even get adjunct teaching jobs. It's about the demand, or lack thereof, and the available supply of qualified people.