I have a theory as to why: Most other departments get to enjoy the "PhD glut" allowing them to score candidates from top graduate programs and then pay them around $60K/year, and then filling things out by with adjunct professors who are often paid in the range of $1500-$4500 to teach a class for a semester. It's why it's not unheard of for adjunct profs to be on some form of welfare to make ends meet.
I suspect it's far more difficult to recruit Computer Science PhDs who will work at these prices, so they probably have to rely on more expensive full-time, tenure-track faculty who likely are paid more than their peers. If you're passionate about teaching or your area of research, you'll probably cope with the lower pay - but that greatly narrows the pool of applicants, especially when FAANGs will pay you 5x more to work for them.
I suspect it's far more difficult to recruit Computer Science PhDs who will work at these prices, so they probably have to rely on more expensive full-time, tenure-track faculty who likely are paid more than their peers. If you're passionate about teaching or your area of research, you'll probably cope with the lower pay - but that greatly narrows the pool of applicants, especially when FAANGs will pay you 5x more to work for them.