All rules are to speed an evacuation from the aircraft. Blinds open so the crew(and you) can see if smoke ,fire, or debris exist or indeed to notice them at all if unaware of any problems. The cabin lights are dimmed to match the outside lighting so that when an exit door is open, your eyes do not need time to adjust to the lighting conditions outside. The next question, why seatbacks up, done so you do not impede the person behind you from exiting the aircraft. These rules may seem silly but look at how long it takes to board an aircraft, then consider you may have 60-90 seconds to escape it.