Which detail from “Thomas Edison: The Master of Improvement” explains why Swan’s lightbulb failed to be successful?

“He developed and demonstrated the first small lightbulb in 1878.”
“Its glow was produced by electricity passing through a filament, or tiny piece of material.”
“The inside of the glass bulb was a vacuum. In other words, it was oxygen-free.”
“[The] bulb did not glow for long, however. It produced light for only thirteen hours.”