I grew up writing on blackboards, so obviously this is purely my subjective preference, but I also find blackboards much better to think on than whiteboards. One thing I particularly don't like is that I tend to write quite fast; the faster you write, the more likely it is that a marker will leave a thin, washed out, barely legible stroke, whereas chalk is always nice and clear. I also tend to leave things up on my board for a few days, after which a lot of dry erase markers become a pain to erase, whereas chalk always erases nicely.

I have a whiteboard in my office, but if I could get it switched out with a blackboard without bothering my nice office manager who already has way too much work to be bothered by my weird requests, I'd do it in a heartbeat.