If you check the source (not the DOM) the actual content is loaded in `<div hidden="" id="S:0"> ...` which is then moved/copied into the proper main content div in the DOM using a JS event it seems.
I used to try EWW sometimes, but it sometimes made whole Emacs crash at unpredictable times, so I stopped trying to use it. But good to know, maybe I will try again in the future, hoping it becomes more stable/safe.