Because there are idiots out there that think there's no difference between the gothic subculture and the emo scene. Plenty difference!!

Gothic people (generally, not saying ALL...) are into dark romanticism, poetry, fantasy, renaissance/victorian fashion, tragedies, and they're actually very mellow/down-to-earth. It's not religion-based (although they've been stereotyped as satanists, pagans, athiests, and practicioners of wicca). Some are very mopey/sad but unlike emos they're not trying to make a lot of noise about it; in fact, they really don't complain that much, they mostly celebrate their disconnection from the corrupt norm of society. Though they may make complaints it's usually because they're being attacked/discriminated against. Also, Goth wasn't sparked by some kind of music scene like emo was.

One example of someone getting the two mixed up:

This satire clip--> [link]