Loading and cost. 1um isn't required to make your car live long. 1um would require a very big filter to last for any length OCI. It would be very expensive and have to be changed often.
They had 20073 P-Plus for 2.38 at Advanced last night!
I bought one for my final dino changeout prior to beginning synthetic 5000 mile OCI. It should handle the final 2500 miles until I start running synthetic.
I saw they had several Purolator L20073s at Advance today. I almost bought another one but I've already got about 20 of them. Maybe it wouldn't hurt to get a few more?
I could have on my old 92, but the new 2005 Hyundai Accent doesn't have room for a filter as wide as an FL-1. Plenty of room for a longer filter, however. I installed one of the 20073 filters I bought last week with my change to 5W20 Havoline SM dino. Took my capacity to 4.0 QT on the button, instead of the OEM @ 3.6, a MOST inconvenient quantity, given the standard Quart bottle. Who needs 3 or 4 tenths of a Qt of oil hanging around, anyway? Temporary reprieve in any case. When I go to 5000 mile OCI, it's back to the tiny OEM filters anyway.