Genie, the media exists only for the purpose of making money for its owners. Headlines (especially) and other "news" content are written as they are to attract and retain readers/watchers...aka, buyers of advertised products. They would call killers "fluffy bunnies" if that would work better.

That being said, (IMHO) the "terrorist" label is more likely to be used for a criminal who belongs to a group which espouses a specific anti societal agenda than to one who is acting on his/her own. Exceptions exist, certainly.