Why not just use CSS-in-JS at this point? With functions and if statements, you now have two full Turing-complete programming languages in the browser. Why? If

Why not just use CSS-in-JS at this point? With functions and if statements, you now have two full Turing-complete programming languages in the browser. Why? If the problem is JS bundle parse time, couldn't you just have a special kind of <script> tag that opts out of compilation and runs in interpreted mode only, and stick your layout JS in there? Having two entirely separate languages seems like such a waste of effort both on the platform side, and on the web developer side having to learn so many things.