The average seat width measurement all goes back to about 30 or 40 years ago when passenger travel was really starting to take off. The airlines looked around for some kind of government requirement on how wide the seats needed to be. The only thing they could come up with was from the Coast Guard, which specified that; the seats in a liferaft needed to be a minimum of 17 inches wide to accommodate an adult human being. So today we are jammed into those tiny seats based on old Coast Guard requirement, though if it really were a liftraft we were talking about, I don't think people would grumble about how wide the seat is.