I heard many years ago that the reason for 50 cycles instead of 60 was safety related. 60 cycles is more likely to match the rhythm of the average heart which makes getting shocked more likely to cause heart arrest. 50 cycles is out of rhythm and is less likely to do that.
Someone I consider a master woodworker once told me that a master woodworker is not someone who never makes mistakes. He is someone who is able to cover them up so that no one can tell.