Welcome Visitor! Please take a few seconds and Oil pressure is "back pressure" not oil pump pressure.
The oil pump does provide the flow of oil, but the bearings and passages restrict that flow, that's what the oil pressure is.
Flow is:
oil pump>>----high pressure by-pass>>----oil filter>>---oil pressure 'sensor'>>---main passage>----bearings and smaller passages.
There is 0 oil pressure from pump thru filter, there is flow but no pressure, if oil filter was clogged there would be pressure, that is what the by-pass is for.
If you put a pressure gauge on the end of a hose and turn on the water with hose's end closed, you would read say 15psi water pressure, now if you open that hose all the way pressure would drop to 0, alot of water would be coming out but pressure reads 0???
You were measuring back pressure in the hose, because of the placement of the oil pressure 'sensor' it measures back pressure as well, the flow coming in from the pump is a greater volume than can be pushed out so back pressure develops and oil pressure sensor reads that.
If I hooked up a manifold with 4 outlets to my hose with the pressure gauge.
And then opened each outlet slightly, I would show maybe 8psi of pressure, because less water is flowing out than available from the flow.
If I were to open 1 of the 4 outlets all the way, pressure would drop to 0psi, and flow would also drop at the other 3 outlets, because pressure dropped.
This is what happens when you spin a bearing, the gap at that bearing becomes larger and more oil can flow out, this drops the back pressure, reducing flow to other bearings, and because of gravity the top of the engine gets even less pressure so rockers/push rods start to tap
