Rails and React aren't comparable technologies. Most Rails developers are using some sort of front-end framework (whether React, Vue or something else) for at least a significant portion of their code. Virtually all React developers are going to work with a backend of some flavour.
For better or worse, the days of writing web applications that primarily ship HTML from server to browser are long over.
Ignoring that, I do think it's fair to say that "Rails does something that most other frameworks don't", which is provide a batteries-included, convention over configuration framework that makes a lot of decisions for you and lets you work with an extremely flexible language. That may not be everyone's cup of tea, but that's not what the Javascript world is selling right now (quite the opposite).
For better or worse, the days of writing web applications that primarily ship HTML from server to browser are long over.
Ignoring that, I do think it's fair to say that "Rails does something that most other frameworks don't", which is provide a batteries-included, convention over configuration framework that makes a lot of decisions for you and lets you work with an extremely flexible language. That may not be everyone's cup of tea, but that's not what the Javascript world is selling right now (quite the opposite).