The dramatics, the desperation to declare a flop.
The pre-order effect wore off, as others pointed out this has happened to other artists recently with the drastic drops. Timed with the release of songs from three huge US acts and going up against the juggernaut that is Swift and Trainor right now, it explains the sudden boot from the top 5. But the song is still increasing and stable in the top 10 and is still doing well internationally. Most of their lead singles were released with a video soon after if not at the same time so they aren't benefiting from a video effect here at all either.