At least on the web, this is a feature, not a bug. It allows the user to modify the page as they see fit. For example, ad blockers or "dark mode" extensions wou

At least on the web, this is a feature, not a bug. It allows the user to modify the page as they see fit. For example, ad blockers or "dark mode" extensions would have a much more difficult job if websites were delivered as optimized binaries. I specify "on the web" because almost all browsers execute the content retrieved from the website with no user interaction besides navigating to a url. Contrast that with operating systems, which all require separate download + run steps (and often a bit flip in between, to mark the file as executable). That's a lot more friction / time for the user to notice if something is not as they expect or want.