If I use block comments like that in most contemporary IDEs, I find that by default they show the main text in flat "this is a comment" styling, even though they're in principle capable of using different kinds of highlighting for different parts of the file.

Similarly, if I preview such a file on github I get syntax highlighting for the code but I don't get rendering for the markdown.

So I think the advantage of an 'official' way of saying you're using this arrangement would be communicating intent to more-or-less generic tools.