It happens. The warning was probably ignored or forgotten. Keep in mind, a lot of people like Windows because they prioritize what they do with a computer over what they have to do for the computer. Interrupting their work is the last thing on their mind, particularly if it involves relaunching applications and pulling up documents after that interruption. They may have even developed habits such as walking away from the computer thinking that everything will be there when they return (including unsaved work).