Mathematicians like blackboards not just because they smudge productively, but also because: a) They erase quickly. I have attended hundreds of engineering meetings where someone brings out the spritz alcohol and paper towels to try to clean off a white board beforehand. Once the clean space is used, that tends to end the use of the whiteboard for the meeting. b) They foster drawing. Drawing involves fine and quick erasure. You see art on blackboards. You rarely see that on whiteboards.
I have never quite understood how whiteboards captured the market. I suspect some of it has to do with business aesthetics. When you leave a meeting with a blackboard, you carry some chalk dust. Text on a whiteboard seems crisper.