A bit of clever misdirection on Edison's part.
The "secret sauce" wasn't the filament. It was the vacuum!
While the vacuum was essential, finding a filament that would give sufficient light while not burning out in a short time was the real problem. Edison started with using a vacuum. Many materials contained enough impurities that passing an electrical current through them caused destructive failures... some lasted longer than others but Edison was looking for a practical, economical light that would be manufacturable. The carbon filament was the answer.
It was pretty practical. The longest burning bulb in history is still lit in a Livermore, California, Fire House—for 107 years.