alt Hacker NewsLots of important points already posted, from reliability over accessibility to SEO. To add a personal reason: speed. I hate slow computer things. If I open a page I e.g. don't have to use for work or similar (like Google Ads or Linkedin or similar horror shows), and loading the page takes longer than a second, I just bounce.
I built and maintain a static site for a company, and it's just wonderful. It opens instantly (which the search engines like), rebuilding and deploying is trivial, I am not forced to update every week because the JS framework has a new vuln.(There are a few dynamic, JS-based parts that load dynamically and fail gracefully.)
None of this refutes my post whatsoever. The amount of JavaScript to open a hamburger menu is literally around 500 bytes. It can easily gracefully degrade just like your last sentence said. You're going to load much, much more than that by following TFA. It loads an entire new HTML page! This argument just doesn't work here.