I think that was the norm once upon a time. None of my older cars had cabin air filters. I remember one car where I had to remove the blower motor and clean the area behind it, which I think was the surface of the heater core. Without a filter, the heater core got all clogged with dust and pollen and stuff.No cabin air filter on the 2001 Monteros. It just sucks in leaves and dust
My 2002 Impala has a filter, but it's in a strange place - underneath the windshield-wiper cowl. Makes me wonder if the eventual "behind the glove compartment" location hadn't really been thought of yet when that car was designed.