Why bother writing articles when nothing was found?
Because even if nothing was found the outcome allows conclusion on the historical activities at the searched site, provided the search was done thoroughly and in a systematical way. More precisely, it allows to conclude the absence of human activity in metal using periods, i.e. after 2000-1500 BC.
Admitted, proving the absence of historical activity is not as interesting as proving the presence. Still, it can help to create a theory on the past of a place by ruling out activities in metal using times. It can falsify theories and help developing better ones.
In just the same way, it can falsify written sources. For example, sometimes there seems to be a tendency in battle accounts to exaggerate. For instance, they say concerning a Napoleon battle that on that particular spot entire “companies fought for hours at point blank range”. The spot is searched for hours with a detector and only 3 or 4 musket balls are found. At the same time the trash found in large quantities indicates that the spot was not searched before. So it must be concluded that some very limited fire was exchanged before the opponents separated again. Rather than pointing to heroic battles the find distribution can be better explained with an encounter of two small groups of soldiers. Every soldier fired his weapon once and then both opponents ran away in opposite directions.
Such search days do not produce anything for the find cabinet but they help to get closer to the historical truth. Even these cases show what a mighty prospection technique a metal detector survey is. They are everything but a waste of time in my opinion.