Goth obviously emerged from punk, but punk didn't last. The same is true of most subcultures: Hippies are old hat; skinheads have come and gone; grunge is yesterday's news. Why does goth alone remain undead?
Some tidbits:
If it suits you, you can be a goth all your life.
Taking for granted the misery of the human condition, goth turns depression into an aesthetic, a semi-ironic pose — a perfect style for the awkward and self-conscious.