It's a bit odd, isn't it? At some point someone decided to mash fibre together to make a board that was nice and smooth on one side and rough with a distinct pattern on the other...and it's been a smash hit. I had a couple spare sheets of the stuff as a kid to use to rest on for drawing and writing without needing to sit at the table. And I think all my pedal boards have been made from the stuff.
(One day I'll find a thread dull enough that zxcvbnm will be happy. Maybe this is that day.)