A cold start is a very low-flow condition. Because the oil is thick, it very slowly flows through clearances. This causes the positive displacement oil pump to slam open the regulator almost instantly when oil pressure is achieved. The majority of the pump’s flow ends up recirculating inside the pump.
The filter briefly sees the pressure spike that opens the regulator. Then it just sees regulated pressure and very low flow. The media of course is only seeing the delta P if cold oil, which due to the extremely low flow, is at a minimum.