Regardless of the rest of your argument, "[allowing] EU/EEA and just about everyone else use the machines" is not an act of generosity but just a way to save money. It effectively uses far fewer immigration staff to complete the exact same controls with the same chance of spotting people who should not be allowed in. It would be entirely absurd to have those machines and that capability and not to use them as extensively as possible and safe.

As I mentioned in another thread, Schengen plans to also vastly extend the use of machines with their own forthcoming changes, there again, not to be "nice" to British or other visitors but just because it will save plenty of cash. It is simply not possible to use most machines currently in use to complete the more extensive Schengen checks which require both entry and exit controls and therefore, Schengen prefers to rely on stamping until their new procedure is in place.