[pas]

I don't think it's unavoidable, but in practice it is two separate components with markedly different concerns and trade offs.

For example if we don't use any client side JS, use only a templating system, it becomes easy to keep it one project.

Eg. there's NextJS, which is a bundle of React and a NodeJS backed in one project. (And while it provides a getStaticProps and other gimmicks it doesn't really do much to make client-server state sync seamless. I still have to manually write the /api stuff.)