WHY GOV.UK'S EXIT THIS PAGE COMPONENT DOESN'T USE THE ESCAPE KEY

Summary from the TLDR Web Dev newsletter

GOV.UK's Exit this Page component uses the Shift key instead of the Escape key for its shortcut function due to several technical limitations. The Escape key is not a reliable option because it's commonly used by browsers and operating systems for other functions, and its use is not always considered a user interaction by browsers. Other keys like Control or Alt have their own challenges, so Shift was chosen as the least flawed option.