Actually, when you think about it, we have not standardized on power plugs. We have standardized the wall socket and the plug that goes into the wall, at least at a country level. And, by the way, Apple lightning cables use a wall plug that is compatible.
But, look at your appliances that have detachable power cords. They are not standardized. Computer power supplies, for the most part, do use compatible power cords, but that cord will not work with my hand mixer, or my rechargeable electric shaver, or my TV. And, to make it worse, World standards for wall outlets are different across countries and certainly different than the US. So, no, we really haven't standardized power plugs across the world. This picture illustrates that point.
Note how the whole of the EU is using one standard. That is 447 million people and the worlds 2nd biggest economic market using the same standard for the wall plugs, the institution of USB-C as a standard for power to lots of electronics is just another step in making things simpler for people in the EU (All things consumer protection is big here).