Because clicking on a navigation button in a web app is a good reason to window.history.pushState a state that will return the user to the place where they were when they clicked the button.

Clicking the dismiss button on the cookie banner is not a reason to push a state that will show the user a screen full of ads when they try to leave. (Mentioning the cookie banner because AFAIK Chrome requires a "user gesture" before pushState works normally, https://groups.google.com/a/chromium.org/g/blink-dev/c/T8d4_...)