It's just how web works – storing data in URL params to restore the same state later. With React or whatever library you do the exactly same thing. In this case HTMX doesn't particularly stand out or enable anything new here.
This is a generalization from personal exposure, availability bias. It just points out that some people implement things poorly — ignoring that many well-designed SPAs do use URL state effectively. React itself does not prevent or discourage URL-based state, it's just the developer's choice whether to use routing or no.
There are many React SPAs where the address bar URL rarely changes, and I have to find some "share" button on the page itself to get the page's URL.