My math professors all preferred blackboards because chalk is an order of magnitude cheaper than markers. Of course, all of our classrooms had whiteboards. :)

I have fond memories of my favorite math professor, always looking somewhat disheveled, and often with streaks of chalk on his clothes or in his hair. Whiteboards just aren't the same.

Apparently there was a preferred chalk of mathematicians; but Hagoromo chalk just went out of business. A chemistry professor of one of my classes read an article in some journal bemoaning this, so he decided to pick up and try some while he still could, see what all mathematicians were in to.