It didn’t help matters that a lot of popular media revolved around NYC (it’s not quite so NYCentric anymore), a city that had sunk pretty low in the 1970s. For example, police logged 250 felonies a week on the NYC subways in 1979 (worst of all being the 4 train, known as the “Muggers’ Express.”). By the mid-80s, it began to look a bit cleaner, but NYC was objectively seedy and filthy in the 70s. As you’d expect, this crime epidemic was translated to countless movies and TV shows that took place in this setting.
Prior to the 70s, the term “mugging” was rarely, if ever, used. But, soon, it was on everybody’s lips. Subsequently, a cottage industry in self-protection bloomed, with not just classes popping up everywhere, but also a ton of literature on the subject landing on bookshelves. At any minute, a “Scorpio Killer” or “Main Street Mugger” could come out of nowhere, so you damn sure better be ready with some Kung-Fu.