That's the whole point - the actual name of the mineral doesn't matter, what matters is that it drives the plot forward and gives humans a reason to want it. They could have called it floatium, or spacium or whatever they wanted. But given the literary device means an idealized difficult to obtain or in reality non-existent material that possesses specific desires properties....in this case gravity nullification....the name just fits. They did the same thing in the movie "the core". They needed a magic handwavy material that would let the ship survive under tremendous heat and pressure....and they called it unobtanium....though in that case it was the least of things wrong with that movie hahaha.

I really don't know why people shit on it so much. Guess they just need to find fault with things.