I'm guessing your pictured intersections have lower speed limits and tighter geometry. As speeds increase, the amount of physical space needed to enter or cross

I'm guessing your pictured intersections have lower speed limits and tighter geometry. As speeds increase, the amount of physical space needed to enter or cross traffic drastically increases. Even beyond that, as speeds increase, the estimation problem moves further away from human perception into something that would require the perception of a fast predatory bird, so even more space is needed just to be safe. When I think of conversions from 2 to 4 way stops, I think of an intersection in my town where the road was listed at 25mph but the enormously wide pavement easily supported driving 40-45mph comfortably, especially being at the bottom of a steep hill, and people drove accordingly. Completely separate from that is the issue of neighborhood groups trying to get inappropriate stop signs added to calm traffic. Stop signs are only for managing right of way; traffic calming should be handled by changes to street design. Disclaimer: Obviously any answer to this question will be a generalization that doesn't cover all circumstances