That's probably because it's not what gist is made for. Embedding a gist instead of adding a fenced block in your markdown or whatever blog engine you're using is kinda silly for a couple of lines of code.
Author here. I completely agree. Embedded gists didn't have this annoyance when I wrote the article. I figured GitHub could be relied on to not change things up too much, but that's what I get for depending on an external service...