I have no hard data on this, but dry-erase markers seem to be used up more quickly than chalk.

Chalk is also less expensive. As one data point: 48 sticks of chalk for $4.30[1] versus 12 markers for $7.74[2]. I'm not sure about the bulk-price comparison, or if colleges can get dry-erase markers for cheap. Although, many of my professors carried their own supplies as markers left in rooms were usually stolen.

There could be a health comparison to be made between dry-erase marker fumes and chalk dust, but I know nothing about it off-hand.

[1]: http://www.amazon.com/Crayola-Non-toxic-Anti-Dust-Chalkboard... [2]: http://www.amazon.com/Expo-Chisel-Erase-Markers-80001/dp/B00...

Crayola chalk is horrid. I gladly pay premium for well-made chalk (and I suspect most mathematicians prefer high quality chalk), which makes white board markers significantly cheaper.

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.

You don't have to pick up a dozen pieces of chalk in order to find one that sort of works if you hold it just right.

Chalk boards also feel nicer to write on, are easier to erase, and the dust comes off of clothes and hands easily.