Real question, what a couple of the reasons are? I prefer the angled out because you get a wider field of view
I prefer having an unbroken view to the rear with the mirrors, i.e. some overlap between side and center ones. Besides not having a gap, there's also the matter of sometimes you can't see behind in the center mirror e.g. on a hill (roof cuts off view), so the side one often works. Oh and without rear window in the way the view in the side one can be clearer i.e. helpful for seeing if that's a roof rack or Smoky.
Oh and how hard is it to use the mirror to check the next lane by leaning forward a bit? I guess everyone on the forum has swapped the stock belts and is harnessed in?
People saying they use the side view to see if there is a car in the next lane concern me for a couple reasons, one always check your blind spot over the shoulder (motorcyclists in particular will thank you), and two the convexity of the passenger-side one is so extreme that it's unreliable for this purpose anyway on that side.