If they allowed you to opt out, then lots of people would, and their "engagement" would be lower.

I wonder if you could fake out the site...have some kind of extension that puts a bunch of empty lines at the bottom.

Then, because (according to AI, anyway) they're using some kind of scroll event listener to detect when the user is at the bottom of a page....the user would just not GET to the bottom of the page, and the page wouldn't know to load more items.