During war time there is not always the luxury of ceremonially burying the deceased. So people temporarily make graves and depending upon the number of dead, it is quicker to make mass graves. Now with smart phones etc, it is possible to document the corpses and the location of burials. But in the case of the IDF that was in search of identifying and understanding approximately the causes of deaths; for possible hostages, foreign fighters, infiltrated Israelis, and ranking Hamas and PIJ personnel; there was probably a frenzy to dig up any areas of recent graves,.and with haste reburying them, and probably not even in the same location.