I have never, honestly, had much of a problem seeing out the rear window while driving, and I prefer knowing what's going on on all sides of my vehicle, including what's behind me. A car coming up fast behind me can easily suddenly be beside me. Do I have family following me requiring me to adjust how they drive (including when driving non-emergently)? Do I have someone else tailgating me? Removing a rear window means creating a huge blind spot, and there's a reason that shipping trucks puts huge signs on their trailers warning other drivers about those blind spots.
Why are they in the same box? Because I reject the notion that, like what some people say about seatbelts, the rear window is useless and unable to be used.
Oh, and as a manner as an appeal to authority, I've been driving for over 15 years and have never been in an accident.