Its easy to design and build a 40-60mm lens, but a 25mm is much tougher to build, particularl;y a FF version. I'm sure lots of people would like to see one, but the price might be a lot higher.
Also, Canon wouldn't want their higher end WAs to loose sales to a pancake style lens. 40 pancake is cheap enough to find room in alot of camera kit bags as 'a nice to have lens' with decent quality.
My 2 cents.