NASA didn’t spend a single dime developing the Fisher space pen. It was developed by the Fisher company at their own expense, in the hopes that it could be profitable. Yay, capitalism. Lead pencil tips frequently break during use. Carbon pencil lead is electrically conductive. You really do not want random pieces of electrically conductive debris floating around in your spacecraft.

I’m still waiting for my TSO’d pencil to arrive. http://www.rstengineering.com/rst/articles/tsodpencil.pdf