First off, May the Fourth be with you! (Had to get that in there…)
Chalk still stands out as the technology of choice of mathematicians everywhere. Those of us forced to use whiteboards realize the wisdom of the ancients once we have to do without chalkboards and chalk.
Whiteboard markers are much more expensive than chalk; it is hard to know when markers run out of ink (whereas there is no question when you are running out of chalk); and after many uses, they leave a residue on the whiteboard which is hard to clean off. Also, whiteboard markeers have many components which make it difficult to recycle, and produces more waste when they go dry. The markers easily go dry, and one has to be always in the habit of ensuring the cap is on tightly when not in use.
Chalk, on the other hand, just runs out. It can produce dust. And though I have had a dust (house dust) allergy since I was a child, I have taught at a blackboard for 15 or more years, and have not experienced breathing problems with chalk. Chalk stands out on a dark background. A chalkdust-clogged blackboard can simply be cleaned off with a wet sponge and a squeegee.
This is in contrast to using the alcohol-based cleaner for whiteboards. While the sponge can be rinsed after use, a cloth or paper towel soon becomes clogged with the ink wiped from the whiteboards from using the cleaner, and are soon disposed of. This just contributes to a landfill problem.
For educators concerned with the vertical classroom, students can work on these non-permanent black vertical surfaces just like they do with whiteboards.