[muspimerol]

I think the common argument is "complex interactivity". If you have sufficiently complex custom client-side interactivity (e.g. sending, receiving, manipulating and displaying data in the DOM without constantly reloading the page) then something like React or Vue is much easier and more maintainable than a bunch of custom JS. Logic for mutating and displaying data can also live on the backend and use SSR, but it has to live somewhere. I think people like SPAs because you can draw a convenient boundary at the server level by exposing a JSON API, and folks working in HTML, CSS and JS like the component model offered by frontend frameworks (I know I do).

There's also something to be said for consistency. When I walk into a React or Vue app, I can figure out what's going on and build on top of it quickly. Even if they are using a mish-mash of libraries (as JS apps do) the majority of the time you will see similar libraries and patterns used.

All that said, there are many monstrosities built upon SPA frameworks with poor performance that would likely provide better user experience if they were using SSR. But there were also many SSR monstrosities built before SPAs were in vogue.

[datadeft]

This is the most useful comment so far. I tend to agree. However, I still think that most frontend project are perfectly fine with mostly HTML + CSS and a tiny bit of JS.