The browsers native language is HTML. HTML is a markup language and if you feed HTML to the browser it will very quickly render the page with what you give it. But no. Let's not do that. Let's instead feed the browser with JSON and then have the build in JavaScript engine translate that into a pre-formatted output which then gets translated into HTML before it's served to the user. Oh, and while we're add it, let's do the exact same thing with CSS. So, now your simple news article or blog post takes ages to load on a 1 gigabit connection and requires about 3 times as much electrical power even though you're only serving text and perhaps a few images - just because someone though it was a really good idea to make a React app instead of a simple HTML page rendered by the server.