In Philip K. Dick's novel 'Do Androids Dream of Electric Sheep' there are key aspects of the plot of the novel that are completely excluded from Blade Runner, including:
That animals have almost died out, and people keep one or more animals as pets, including farm animals. This feeds into the elements of empathy and the Voigt Kampff test.
That many people in the world follow a technological religion - Mercerism - where people commune with an enigmatic figure through a virtual reality device called an 'empathy box'.
That a shadow Police force exists in L.A. almost entirely staffed by replicants, and that they use an entirely different test for human/android. A blade runner from that outfit directly wonders which one of them (Deckard or himself) are real.
In the novel, LA and indeed most of the planet is now vastly underpopulated, which is another reason why people use empathy boxes and pets to make themselves feel part of a community. This is hinted in the movie in the scenes where J.F.Sebastian lives in a deserted condo, but many of the street scenes and bars are very crowded.
Why did the writers and Ridley Scott exclude these aspects of the original source material, despite them being core to the plot of the novel.