The people in CA-8 (Mojave Desert) have very different needs and concerns from the people in CA-12 (San Francisco) even though they represent the same number of people.
Actually, under Open List PR, you could still have de facto local representatives. Someone could focus their attention on the needs of the Mojave Desert dwellers and get elected or not based on their popularity in the desert. PR doesn't prevent people from focusing their attention on geographic regions; it merely creates other alternatives.