I think what snowl wanted to know was more technical than that - why such new syntax is necessary to achieve those things? Why exactly the same things cannot be achieved with existing syntax? For example, it's very understandable why JSX is preferable over vue's string syntax (<tr v-for="employee in employees" :key="employee.id">) in terms of "just use JS" argument. What exactly warrants this necessity for these weird looking and non-standard syntaxes and why it can't be done without them. Thank you.

With plain HTML+JS, it's very easy to get components to accidentally race each other when you have multiple inputs and outputs, like user interactions plus async API calls plus rerenders and UI state changes.

The syntactical sugar is often masking a lot of complexity behind the scenes, and the very idea of (say) React's props propagation within a component tree is an abstraction over having to write a bunch of separate event handlers and figuring out a way to manually share state between them.

If that is a problem you run into in your app, you can of course write your own system. But that's all these frameworks are... someone else had that same problem, decided to formally tackle it and make it a well-supported & documented system so that others facing the same problem can use that as a solution too. Over time the industry converges on a few (React, Vue, Svelte these days, Angular in the past). If you don't like any of them, well, that's how a new framework is made...

Vanilla HTML doesn't even have loops and conditionals, the basic features of any templating language from 10-20 years ago. It's glorified Gopher with JS shimmed in because Netscape was afraid of losing dominance. It was never intended to become the de facto language of software app distribution... the whole reliance on a "document" model is a poor fit for an entire class of web apps (like Google Maps or Gmail or Spotify or Netflix or Figma or Photopea).

IMO the better question in my mind is not "why do new JS frameworks and templates keep popping up?" (because HTML+JS sucks), but rather "why haven't native HTML+JS continued to evolve, creating a native solution for common pain points that the frameworks address -- like state, component trees, etc.?"

For what it's worth, at least the Web won, instead of (say) ActiveX or .NET or Flash or the Metaverse or whatever alternate ecosystem companies have tried. The JS frameworks offer some of the devex benefits of those other richer languages while still being able to compile down to HTML+JS for delivery to the enduser -- a huge benefit over a "cleaner" ecosystem that would require the enduser to install additional software. The ugliness of modern JS is because it's no longer trying to just handle basic documents, but trying to replace desktop apps altogether. And for many people, it already has.

JSX is not JavaScript, so if you're using it, you're wholly in the "new syntax" camp.

Sure, you're right about that. It's just that everybody, for example, has the option to use React.createElement directly without JSX, as it's just a syntax sugar and people use it because they prefer it over the other option. Let's consider Vue's syntax:

    <template v-for="todo in todos">
        <li v-if="!todo.isComplete">
            {{ todo.name }}
        </li>
    </template>

Genuinely, do developers have the option to "just use JS" here (for looping and conditional)? I personally think this Vue example is very inferior to JS and I see it as an unnecessary complexity unless this "weird string magic" is what enables some nice-to-have feature which is not possible with plain JS.

You can write render functions manually in vue too.