Like autumn leaves falling from Hollywood’s once-evergreen trees, a familiar cycle is returning to American entertainment. For years, the industry insisted its experimental season would last forever, that audiences would adapt to whatever programming executives deemed necessary for our moral improvement. But nature, like the marketplace, has its own immutable laws. The entertainment industry has been quietly recalibrating its priorities lately, though you wouldn’t know it from the panicked press releases flooding out of activist organizations. Television networks and streaming services, those great barometers of American cultural preferences, are making decisions based on an almost forgotten metric: what viewers actually...