Butter does melt, try it in the microwave ---- .
Butter is a water-in-fat emulsion, when it heats up the fat melts.
The easiest way is in a microwave and half power at 60 seconds. Or if a stick of butter, try 30 seconds. The butter will still retain its shape even after melted. SO you need to take it out and stir...
On a metal spoon? well because the metal heats up faster then a plasic spoon, and plastic melts.
Oil is already liquid so it wins.