Because he doesn't know how to tune it properly!!!!
mine will detect from 1 - 1 1/2" when properly tuned.
problem is it needs tuned every time you turn it on.
OK, I'll bite, what is this proper way to tune the Fisher/BH? Turn it on, adjust til it just stops beeping. 1/2" range, tops. Micro-adjust til it's at the hairy edge of beeping (or falsing) and maybe get another 1/8".
Adjusting the interior pot only seems to affect the position that the external knob stops beeping, but has no affect on range.
Maybe you got a rare one with much better than typical range???