Please explain what unique features those two platforms have which oldschool forums couldn't already do without JS. Not to mention you are posting this on a platform which works quite well without JS, including support for folding subthreads and upvotes.
> even a modern ecommerce store could not work with simple html these days
What is required for an ecommerce store to be "modern" in your view? Because I can't remember a single important part of Amazon which works only due to JS. Sure, that image pan/zoom feature for product photos needs JS, but that feature is also worse than just opening an image file in a new tab and doesn't even work half the time. Amazon also still reloads the entire search whenever I check a filter checkbox, making it annoying and slow to set multiple filters. Another case where poorly used JS actually made it worse than a simple HTML form.