Why doesn’t my Plymouth Duster have a passenger side mirror?

My '70 Duster never came with a passenger-side mirror, kind of freaked me out at first because I learned to drive in a '03 Chrysler minivan and got used to using outside mirrors. But I was able to get used to the Duster pretty quickly and haven't had a problem in the 14+ years I've had the car. I do angle my inside rearview mirror slightly to the right to give a better view out that side of the car but I never feel like I can't see enough around me when driving. The c-pillar blind spot isn't as big as it seems and I can always spot someone on my right pretty quickly with a quick glance over my right shoulder.

The backup cameras and blind-spot-warning lights on newer cars are nice but the irony is the gov started mandating those because side and rear visibility is so piss-poor in cars made after about 2010, even if you try to turn your head and look around you can't see ****! Crossovers are the worst IMO but there isn't much about those in general that isn't terrible.