Theories (mostly relating to physics)
-- more vertical angle of rear window combined with less aerodynamic airflow from longer roof length. Sedans tend to have shorter roof and probably better air flow down the more 45 degree angled rear window.
--Maybe a function of distance from driver POV-- the SUV rear window is further away, thus 'smaller" in rear view window; more important to keep it clean of raindrops.
-- Maybe just the ability to put the motor and wiper mechanism in that big rear door; this would be more difficult in a sedan-type car to put it in the trunk or on the roof.
Incidentally, I think I remember some sporty hatchbacks with very angled rear windshields having rear wipers back in the 90s...