A proper FE developer who knows about accessibility (not just ARIA-attributes but also contrast and usability), UX, semantics, and also being capable of delivering performant user interfaces is rare these days, because people think full-stack development really is a thing. I think it is one of those mythical things like a 1000x engineer. People think that they can get away with 90s style websites, but please test stuff with a screen-reader, and also while you're there get some front-end consulting, you will be surprised how badly you may be doing. IMHO, many need dedicated FE development. Whether they use React or not, I think many do. You can distribute many responsibilities on non-technical members of the team, but then you start thinking "couldn't they just learn a bit templating so I don't invest so much time on implementing their seemingly never-ending requirements"!
BTW, this separation is of course also possible with your traditional MVC stack, which I also use in my personal projects a lot, in which React is indeed overkill, and there are many cases that a bunch of templates deliver all the things you may ever need. If it gets complicated enough some day, return your View Model as JSON and there you have a perfect API. IMHO REST APIs aren't suitable for any dynamic front-end development anyway.
The only reason I wrote that single sentence in my previous original comment is that React forces your hand a bit, in this matter. It's a small point among other things.
It also doesn't end there. There's the UX part, re-usability (huge difference to have a cross-team front-end service-team), performance (not just initial load... Are the widgets you build with, say, Alpine.js tested for performance?), development speed, caching, offline-capabilities, opportunistic rendering, other best practices, branding, consistent design and interaction and so on. It's a science on its own.
Front-end is not just some basic thing which got a complex solution for no reason. It is a complicated task.
I think people approach it with prejudice (ew, Javascript!) and never properly learn it.
There are projects where react would be overkill but many benefit from the clear separation of the front end.
Also configuring a react project is easier than many other projects I've seen in my career. People just love getting internet points by constantly talking about left-pad, node_modules size, config files etc. I personally know how crazy managing maven or gradle (.gradle folder hell) or nuget or composer or pip (venv or virtualenv...) or [name of your favorite package manager] can get, so I'm thankful for the great community that work on the problems with the npm.