What do you get out of evaporated milk that you can't get from milk?
The surprising bit is how far you can get into a meal that looks right before you realise it really is not.
I sometimes buy evaporated because it is a big time-saver, but never sweetened condensed because it's quick and easy to add sugar myself, and leaves me in control of how much relative to the other ingredients.
Both are thicker, creamier, and even sweeter than milk - because even without the added sugar the natural sweetness of the milk is concentrated by the reduction, removing all that water.