How do you server-side render something like a chat app? You'd still need a fair amount of client-side JS, right, unless you want to reload the page every time someone hits send. I remember old sites that worked that way.

React is easy and intuitive. No templates, and I can change the HTML however I want in response to what the user does. Not that I do fancy things or enjoy single-page apps, but even if you have that, deep-linking is easy.