Many possible reasons. A crude bulb with a thick filament will last longer, as the current per unit area goes down. A thicker filament would of course drastica

Many possible reasons. A crude bulb with a thick filament will last longer, as the current per unit area goes down. A thicker filament would of course drastically increase the life. And reduce the voltage by 10%, an incandescent bulb will last 10x longer. With Tungsten the usual failure mode is excited evaporated material cooling and ending up on the cool bulb wall, this is the "blackening" you see on the bottoms of bulbs. Tungsten is a pretty amazing material, but will wear down over time.