Proving cast iron pans
No idea why it works, but I learned a variation of your method from a junk dealer in Chicago:
Coat bottom of cast iron pan with veg oil. Cover with just enough salt to be absorbed in an even layer. Heat on high until it smokes so much you grow worried the neighbors will call the fire department. Turn off heat, let cool down and wipe out.
This made a small skillet slick enough to release fried eggs like a non-stick pan, but the coating didn't last very long. I suspect it would have to be repeated much more often than a typical cure to maintain non-stick properties, and I lack the patience to do it that often.
So, yeah... Why does this work?