Why can’t we ID these people?

Heritage Action, with what seems a perfectly valid question: 'Why can’t we ID these people?'15/10/2017. Here's one metal detectorist pictured at Great Chesterford:

And, as HA point out, this is just one percent of the 24000 active detectorists postulated by Dr Sam Hardy's  latest calculations*:

In other words the serried ranks would look a bit like this in overview:

One, a hundred, twenty-four thousand. How much information is being lost weekly, monthly, annually as artefacts by the million disappear into their pockets? Why is there so little discussion of this?

*The Heritage Action Artefact Erosion Counter has at the basis of its algorithm a figure well below half of that, the PAS suggest its 'around 9,600 metal detector users across England and Wales', while until I saw Dr Hardy's figures I was using my own more recent revised value of 16k. What's yours?