I remember learning separation of concerns and then react popped in and just threw that out the window and yet everyone adopted it. I still haven't recovered from the idea that these guidelines are very bendable etc.
A component with its styling, markup structure, and behavior, is one concern. These components can than be combined and nested in every which way you need, they are very modular.
If you separate concerns into markup, styling, behavior, than this form of component-based reuse is difficult. But it could conceivably be easier to reuse an html template or css class for different features.
Hooks are also a way to separate concerns in a different way than lifecycle methods. Lifecycle methods group code by specific points in a component's life, but then the logic can't be extracted and reused. Hooks on the other hand encapsulate reusable logic that can then be used in different components.
Unfortunately, in capitalism that’s too much to ask, because it would improve everyone’s lives except the ad industry’s.
Perhaps some sites can be excused from this because they really do fall on the app side of the document–app spectrum. Google Maps comes to mind, but Facebook? They’re just bad internet citizens.
Did it though? I've worked with React for some time, and we simply put all the non-view things into separate modules, or at least separate functions. React is (still) a library, it doesn't prevent anyone from mixing the layers and making spaghetti.