Our designer wouldn't have been able to deal with HTML markup within the JS files in React. Having the HTML and (S)CSS separated out made life much easier for him in Angular.
(edit: Naturally downvoted due to being slightly critical of React on HN. Which happens every time.)
You are being critical of separation choices. To which I am curious why embedding the CSS and HTML inside a Javascript file makes any difference to the designer? In practice, we often see slightly different syntax to accommodate, but I cannot imagine that is a true barrier. The CSS and HTML (or their slightly modified equivalents) are still logically separated from the rest of the logic in the file.
He has no idea about how the TypeScript/JavaScript files work. He doesn't really have to touch them, unless to maybe see what extra data the component model contains if he wanted to dig deeper and display other things.
If the designer was handed an HTML page with <style> tags embedded, I cannot imagine he would fall down unable to figure out where the CSS is, and this is not much different.