It's on the right side of the car so folks that walk by when it's parallel parked along the curb would see it. Consensus was (and pretty much still is) that most walk looking downwards and the pentastar was placed on that side and low so it could be easily seen and be associated with the Chrysler product. Some say it was for the passenger to know the car was a Chrysler product since the driver already knew, but that's not the case.
Notice now that later GM cars have the emblem on the fender now too
Cheers
Dave