I guess cable kinda took over after the 80's

I would imagine that after the 1990s, shares (of an audience watching a broadcast TV program) essentially became meaningless, because of the rise of cable channels, and later, those cable channels launching original scripted programming. After then, all that mattered was the number of viewers, rather than the number of households or shares, and around the mid-to-late 2000s decade, the percentage of people within the 18-to-49 demographic watching a certain broadcast TV show started to matter even more than the total number of that show's viewers.

By the late 1990s, only the scripted programs that have the biggest audience figures would get above even a 20 share. I think it's hard to imagine the most-watched scripted broadcast TV shows of today can get above even a 10 share of the viewing audience.