Its hard to see why the JS frameworks came to be, and easy to see the up front complexity of most of them. People who started before good frameworks were around take it for granted that people know what happens when you build complex sites with vanilla JS: You get a mess, or you get your own framework.
Not everybody wants to render everything on the client. JS frameworks (vue included, despite trying) do just not support rendering as a simple page.
Some people do have light needs that won't ever require a full framework.
Other people have very heavy needs that will require their own frameworks. The JS ones (react included) are not absolutely flexible.
And, if you fit none of those categories (honestly, most people are on the first), just replace the title with "how does a JS framework operate on the DOM", and take it as a learning resource.
> Not everybody wants to render everything on the client.
No, and then you should just render it on the server. Most "apps" should not be JavaScript apps at all. However, once you do need to enter that territory you should definitely use a front-end framework.
