"Apps that you "live in" all day have pressure to become everything and do everything. An app for editing text becomes an IDE, then an OS. An app for displaying hypertext documents becomes a mail reader, then an OS."
The real question is why the OS can't do the job of the web browser in the first place. Has anyone ever tried integrating one so that people could use web pages in the same native integrated way as programs, opening them like say, a file manager would open directories? I guess Electron, but that doesn't really count given that it's just a reskinned browser.
So browsers implement their own tabs and so browsers are basically becoming a second window manager. Once you have this it is natural to consume more "applications" to fit into your window manager. The web is a powerful enough feature to start this process.
I wrote about this a while back https://kevincox.ca/2021/01/11/tabs-were-a-mistake/
The opinion whether it's good or bad also varied.
I vaguely remember saving web bookmarks as files, and using the built-in browser to navigate them to them. The shell (WPS) had the philosophy: "everything is an object".
It was very cool for its time.