Why did the weakening of some subcultures allow their slang to spread more widely?

The weakening of a subculture facilitates the spread of its slang because it increases the frequency and nature of its contacts with the dominant culture.1

When a subculture is structurally tight, its language—often a specialized argot—remains contained within the group, with little leaking into the broader society. However, as a subculture weakens, these internal barriers break down, leading to increased interaction with the dominant culture. This heightened connectivity allows the subculture's unique vocabulary to diffuse outward, where it is often adopted as slang by the general population.1

For example, while highly insular groups like the Mafia have historically contributed little to the general lexicon, other groups that have experienced shifts in their social standing or structure have seen their once-secretive terms become widely used. A notable instance is the language of criminal narcotic addicts; as their subculture became less isolated, terms that were once highly specific to their internal experience were adopted and used freely by the broader public, including middle-class teenagers who had no direct connection to the original context of the words.1