There are some reasons why I don’t buy into it. Performance is one of them, like choosing CSS-in-JS is some automatic performance win. Part of the problem (and I’m guilty of doing it right here) is that CSS-in-JS is a wide scope of solutions. I’ve generally found there is no big performance wins in CSS-in-JS (more likely the opposite), but that’s irrelevant if we’re talking about something like CSS modules with the styles extracted and linked up like any other CSS.
I’m more familiar with the Elm ecosystem and over there we even have Elm UI which conflates both HTML and CSS, abstracting things away even further.
I’ve started using CSS in early 2000’s so for me it’s second nature to write style information that way. Still I believe there’s room for CSS-in-JS or better CSS-in-Whatever. It depends on the context of the project, really.