I want to believe someone got to a good stopping point in this book - looked around - and realized that putting a taco in there was their best option
From Vice:
"Don’t have a bookmark? Try using a taco," Amanda Mae tweeted. "(Actual photo of an actual book found in the book drop at my library in Indiana a few years back)."
The cursed image that she attached showed some kind of meat-filled taco flattened in the center of the book, ringing the two adjacent pages with an awful cheese corona. "[Y]ou legit COULD NOT TELL!"she replied to someone who expressed concern about this absolute crime. "It was so flat in the book, it had to fall open to this page for it to be noticed!"