I had a similar issue recently and Walter pointed out my misunderstanding of the Reader Function in Safari for me - no doubt he will chip in if i’m wrong.
The appearance of ‘Reader’ is dependent on the amount of text that appears within the div on the page. As your first link points to a page with far more text than your index.html page, i would suspect that is the reason.
You could text by adding more text inside the same div to see if it triggers the Reader function.
I am not sure what the text character count is, but you will soon see.