I did classic server side rendered apps, but experimented with pure JS apps early on where the only way to get persistence was to store things in cookies. The "app" was just a html file on the desktop that you double clicked on to open in the browser. Then came AJAX. and during the last fifteen years more and more pieces have fallen into place to make web apps more viable, like service workers, local storage, add to desktop, etc. But JS apps are much harder to develop compared to server rendered app, because you have to manage state, while server rendered apps are just a snapshot of the database.