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

I learned to drive & parallel park in a 1 ton chevy box body truck, side mirrors only!
My Valiant had some aftermarket mirrors on both sides when I got it. After paint I used these repop tri-five Chevy mirrors. The passenger side has a convex mirror.
Note that the passenger side is mounted about 2" further back than the driver side to clear the windshield post from blocking the vision, and the vent window does open. I was told that passenger side mirrors were a dealer option as part of a towing package.
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