The view out the rear glass is up way too high on the new suv/crossover vehicles to give a reasonable view of whats behind.
For that reason alone is why they're necessary I'd obviously guess.
I've heard people say they'd rather have lower and bigger rear
glass like the older cars had too. I'd also guess that won't happen any time soon. Even the front of some late model vehicles, Camaro comes to mind, are getting hard to see out of. The angle between windshield and dashboard is such that the view if the road is limited to almost tunnel vision. Just my observations.. I'm sure aero dynamics is part of the equation that dictates why the viewing areas
are such. Maybe when they perfect the collision avoidance function/system
they'll install front cameras too. Then there won't be a need to look out the window.
Please excuse my sarcasm.