[CharlieDigital]

    > I wonder whether you've ever tried to make a non-trivial SPA without them.

I personally have. React launched in 2013. Here's a real-time enabled browser chat app I built in 2011: https://www.youtube.com/watch?v=WG_W0VxjzbM and at this point, it had been years of building similarly complex JavaScript apps.

Many sufficiently complex apps existed long before React. The "OG" Outlook Web App was certainly not lacking in complexity.

The challenge is that it requires far more skill and a deeper understanding of DOM, JavaScript, and CSS. It requires being more diligent about encapsulating logic.

What React did was it made front-end more accessible to a wider audience. The skill barrier is lower (though traded for complexity elsewhere, IMO). Devs now probably start with React and Tailwind before learning raw DOM and CSS. The good ones will eventually learn it, the mediocre ones will vaguely know that it exists.