Phoenix started building car-friendly neighborhoods starting in the 1920s. Originally, wide boulevards and shady sidewalks were included in the design of neighborhoods, but these quickly went away. Why waste space on something no one is going to use? By the 1950s, many neighborhoods were built without sidewalks at all. This practice continued for decades, until there came the realization that people, and especially children, sometimes needed to walk, and doing it on the street could be dangerous. My neighborhood, which was built in the 1980s, has sidewalks on one side of the street, which was a compromise. After that time, sidewalks were considered an important part of any good neighborhood, so any subdivision built in the 90s, 2000s, and 2010s made sure to include them. Sometimes with winding paths and shady trees!
But most of the Phoenix that people use has no place for pedestrians. The sidewalks along 67th Avenue, for example, have nothing between them and the cars going by at freeway speeds. And unless the city of Glendale decides to close a lane in each direction, which isn't very likely, that tiny sidewalk is all that will be there for the occasional pedestrian.
But this is Phoenix, nobody walks in Phoenix!