Technically all JS also lives in the HTML document. All JS is either in HTML attributes, in HTML script blocks, or referred to from HTML script blocks. The HTML

Technically all JS also lives in the HTML document. All JS is either in HTML attributes, in HTML script blocks, or referred to from HTML script blocks. The HTML page was always the boss. There's simply no reason for what's done here. Also, reminder, one reason why we like external assets is because they don't change (as often) while the HTML document is often dynamic (and hence not cacheable).