Is it really? You might as well say it's been a disturbing trend that developers aren't familiar with assembly language anymore.
As abstraction on top of abstraction is created, it becomes easier and easier to write software, so naturally there are now more frontend devs who aren't familiar with web dev basics. And if all you have is a hammer, every problem will look like a nail. Similar trends happen for backend devs and in devops. Is that really a problem? Only if you are a company that hired them with different expectations.
React solves multiple problems, sure. But I would say that templating isn’t one of them, and it definetly isn’t an abstraction to something more obscure.
You have this on the backend and devops side as well, but I would argue that most competent developers there know that there are other solutions.
Maybe my experience is more skewed towards front-end developers, but I would make the same statement about backend devs if they instantly choose one technology over the other, simply because that’s all they know. (Not even because they can defend that technology with reason)
As abstraction on top of abstraction is created, it becomes easier and easier to write software, so naturally there are now more frontend devs who aren't familiar with web dev basics. And if all you have is a hammer, every problem will look like a nail. Similar trends happen for backend devs and in devops. Is that really a problem? Only if you are a company that hired them with different expectations.