I wonder if some of these findings are due to dodgy/home spun garage power installations. There is a maximum distance apparently above which the local house mains ground is not acceptable. The armoured cable sheathing ground feeding an outbuilding is broken at that end and a local ground rod used instead for the benefit of local RCD and safety in general.
Quite possible - when I had my workshop overhauled last year the electrician insisted it needed it’s own ground rod separate from the house - a 1m copper rod sunk into the earth.
