I suppose if you spend most of your days in bed, there would be no need for a living room. But a lot of people spend their days in their living room - watching TV, reading, having friends round for coffee.
It's called a living room because that's where people spent more of their waking hours than any other room. Kitchens were used for cooking meals, rarely for eating meals in them - that came later. Dining rooms were where people ate. Bedrooms were for sleeping.
Maybe because I watch TV, read books, mess with the computer, read the newspaper, do my puzzles, etc, in the living room and NOT in the bedroom. I have a casual living room, for LIVING, if you do not need one rent an efficiency.