There was no single conscious engineering decsion that went into chosing 60Hz vs 50Hz, it was economic. Long distance distribution of AC started in Europe with AEG, a partner of GE/Edison, using 50Hz for transmission, but was used as DC for the most part. But Edison insisted on promoting DC over here for too long because he wanted to keep it under his control. When AC took off here in spite of his efforts, everybody had their own ideas of frequency, because most early systems were converting steam engines or water turbines so the speed of the prime mover was already in place. So hardly anyone matched; there was 10Hz, 25Hz, 33-1/3Hz, 40, 50, 60, 133, etc.etc.. When GE got into it, they settled on 40Hz at first because Edison's research on flicker for moving pictures showed that's where the human eye starts to not react. Westinghouse was selling 133Hz arc lighting sysyems, but that was too fast for Teslas motor technology at the time, so they settled on 60Hz as a compromize between Tesla's original 25Hz motor designs and lamp flicker. However Westinghouse was way ahead of the game with Tesla's AC motors, so when they changed to 60Hz motors, people started ordering 60Hz generators. Edison first tried to get people to use 50Hz by bringing in AEG generators, but it was too late, Westinghouse had the drop on him by virtue of shear volume of production. When standardization came about later, there was such a pronderance of 60Hz motors out there and it would have cost too much already forbpeople to change so it dominated the process.
