Prior to Senator Kassebaum's bill, there was no US law governing locomotive or railcar headlights. As a result, some commuter railroads and transit authorities equipped MU cars with dual, lower headlights, European style. After her bill became law, these rail lines had to add a third, centered, high headlight to the MU cars, as the bill required a distinct "triangle".
So, the reasons for their use in the US and Canada did differ materially. I got involved in this as I worked for a short line with no need whatsoever for additional locomotive lighting - we already had operating Mars lights on all our power. So, it was just peeing money away as far as the AN was concerned.