That's certainly part of the domain of react applications. But there are a lot of react applications that aren't (really) in the domain of HTMX, like "local first" applications or other applications that rely heavily on browser js APIs.
It's a little like comparing HTML and JavaScript, isn't it? React is a JavaScript library (in the sense that you write your own code that calls React functions). Whereas HTMX doesn't integrate with your application logic at all. It provides a mechanism for placing your application components on the screen.