Who are "they"? The aftermarket ones have their place....not in dusty muddy environments and not left neglected as long as you can paper. My car has had a K&N all it's life. It is a pavement machine and it gets driven mostly in an urban are with large expanses of cement and grassy lawns. The oil stays as clean and nice as the truck with oem filter and intake and it is prerunner so same driving environment. If I had 4wd and/or lived in rural environment or desert where there would be much more dust/dirt around, I would stay stock with paper filter. Just like everything else, it has it's place and one thing doesn't fit every need. Track vehicles no runny z papuh eh? Keeping things in perspective is never detrimental..............