Abandonment probably occurred due to a military or other national crisis. Contrary to the modern agitprop, ancient Egypt was not politically stable for thousands of years. Still isn't.
I have no dog in the hunt between “abandonment” and your comment that the greatest mystery is how they got those boxes transported to the niches inside the ‘temple’ or whatever it was.
It seems to me that we could all agree that there are mysteries in the construction of tombs and monuments in ancient Egypt that are difficult to explain with the old standard arguments of “infinite number of workers’ pulling an infinite number of ropes or hammering away with hard stones for an infinite number of years.
I HAVE NO IDEA WHAT THE ANSWERS ARE, BUT I’M NOT SO VAIN AS TO CLAIM THAT I DO OR THAT THERE ISN’T ROOM TO QUESTION THE OLD ARGUMENTS WITH SOME FACTS THAT TEND TO RAISE MORE QUESTIONS.