The back button is one of the greatest inventions in the history of usability. It's the centerpiece of the thick user agent, and the user agent is why the web took over the world.
The web is a platform for modal applications with addressable state. To meet the expectations of users, any app on the web must somehow shape itself to that model.
BTW have you ever used a navigation based app that didn't have a back button? Try the native YouTube app on iOS. It's infuriating.
...but the native YouTube app on iOS does have a back button: obviously there's something important about navigation that "stack of pages with a back button" isn't sufficiently describing.
The web is a platform for modal applications with addressable state. To meet the expectations of users, any app on the web must somehow shape itself to that model.
BTW have you ever used a navigation based app that didn't have a back button? Try the native YouTube app on iOS. It's infuriating.