The problem is likely from the oil pressure staying very close to the sensor's ON/OFF level/point. So you've had the oil pressure basically hover at that special level that made the sensor change quickly from on to off, to on etc, enough to bounce the gauge needle over the bottom pin.
These later Fords don't have a true pressure sensor any longer, the sensor produces two possible signals, On or Off signals. So the gauge is simply reading one of two levels, either near the left when there is too little pressure, or to the middle/right when there is enough. It's a dummy light but displaying as a gauge, showing pressure off, or on.
The older Explorers have a larger oil pressure sensor, instead of the small one you/we have. You can swap to the older sensor, but I don't recall if the gauge is identical from the 95 models to 98+ units. I'm sure someone here has posted what they did to make it work, but it's been a bunch of years, I forgot.