I remember learning that originally all the electric power produced in the US was DC. Thomas Edison was actually a proponent of DC. It was said he did not know how to do the math for AC. It was a German immigrant who pioneered AC and the invention of the 3 phase AC motor helped cement the use of AC over DC.
The first use of AC in the US was at 25 Hz. I guess the generators in those days were not efficient enough to produce 50 Hz voltage. 50 Hz was not chosen because of metric, but because it was twice 25 Hz, and machines that ran at 25 Hz could be easily upgraded to run at 50 Hz.
It was an American clock maker who is responsible for the 60 Hz standard. He could sell his clocks more cheaply if he could synchonise them to the line frequency and if the line frequency was stable and of course if the line frequency was 60 Hz. He gave the presidents of various power compnaies gifts of clocks and in order for them to work or keep proper time, the power companies had to insure the frequency was right and stable. This is what established 60 Hz in the US.
What it all boils down to, was the US settled for convenience and the rest of the world for economy. Resources were in abundance in the US 100 years ago and so conserving was not an issue. Now, it may be, but the standards are established and it would cost a fortune to change them.
Those countries that the US played a major role in electrifying use the same power standards as the US. European colonies tend to follow European voltage standards. Korea is the only large scale industrial country I know of that switched from 120 V single phase to 240 V, using the schucko plug and German socket. But, they still use 60 Hz.
