Well traditionally, cars only had one trunk, now it is common that they have two. The need arose to distinguish them, and ‘front trunk’ easily collapses into a nice single syllable portmanteau that makes communication simple and concise; the language evolves and a new word is born.
I think frunk is a good word. What would you call a trunk that is in the front of the car.
A normal trunk in the back isn’t a “bunk”.
Why is frunk a good name for the front? It’s silly.
Well traditionally, cars only had one trunk, now it is common that they have two. The need arose to distinguish them, and ‘front trunk’ easily collapses into a nice single syllable portmanteau that makes communication simple and concise; the language evolves and a new word is born.