How will someone on a laptop run my website as an 'app'?
Should I download a Wells Fargo app to my desktop, so that I can do banking with them? And a Google Docs app? And a Seattle City Lights app? Maybe a Progressive app, so I can manage my insurance policy? And one for the Washington DMV?
How many problems is running random binaries from random developers at those organizations going to give me? How much more expensive is it to develop apps, over websites? How will you make these apps run on Android, IOS, Linux, MacOS, and Windows? [1]
All of these websites have rich app-like functionality. The web was designed as a document store, yes. This is 2018, though - its not used as a document store. It's the place where I do my banking, my shopping, keep my spreadsheets, and make image macros. Turning all of that into non-web apps will just make development more expensive, degrade my user experience, and negatively impact my PC's security.
But hey, the upshot is that the sanctity of the back button will be protected!
[1] Maybe we could sandbox them... And have a cross-platform 'operating system'[2] where they can run. Maybe even have several such 'operating systems', with similar functionality, but built by different vendors. Vendors like Microsoft, Apple, Mozilla, and Google, maybe?
[2] We can even make this 'operating system' support opening static .HTML pages, so that we can 'browse' through them.
The web was not designed for such use, yet we continue to stretch and abuse whats there and wonder why most sites suck and get it wrong.