I've gotten some razors that have indeed turned up shave ready, even though they were not advertised as such. Yup, poor storage, dinging the edge, maybe it wasn't sharp when it was put away etc are all good answers.

Maybe some are used for alternate purposes (box openers or kitchen knives or whatever) by people who don't value straights for what they are. Maybe someone thumbs the edge or tries to cut various materials to test the sharpness and damages the edge in doing so.