There are about a million exucses (er, reasons). Some of them are legit: older professors often have better handwriting at blackboard; chalk is sometimes bette

There are about a million exucses (er, reasons). Some of them are legit: older professors often have better handwriting at blackboard; chalk is sometimes better for certain drawings; left-hand smear; etc. I suspect the biggest reason is that, in math circles, blackboards have a much larger cool/nostagia factor.