My experience in airframes is only at the small (part 23) end. Sensors would be painful, they fail, their wires fail, their displays fail. On very simple low cost (relative to airliners and biz jets) aeroplanes, we would rather avoid them.
On our programme, the only structural sensors are for temperature. It is theoretically possible to get the airframe temperature above the safe limit for the material (it is pretty improbable, one would probably have to have an all black aeroplane parked in Death Valley in the summer then pull straight to 10g on take-off) so we are obliged to do that. Otherwise we are avoiding electrical content wherever we can.