Because some people don't want those pesky people who are too poor and have to walk to places.

Because that would make walking convenient...nobody wants that

Sometimes to prevent ease of travel for homeless or other loitering activities, sometimes because everyone wants to use tax money for their pet projects and it’s hard to excite people about sidewalks. These are just my guesses

Poor people might walk through their neighborhoods. They might even be nonwhite.

Well, America is the land of the car and that's reflected in basically all infrastructure decitions, be that public transport or sidewalks :/

Neglecting sidewalks is nearly the same as not building them. The sidewalks in my area can be terrible even if the road has recently been resurfaced. There are many locations where wheelchairs, strollers, and walkers would be difficult to use to due to lifted, cracked and chipped sidewalks. Some sidewalks have over grown plants to the point that they are nearly unpassable. In some areas this requires stepping off the side walk and into the oncoming lane and around a blind corner. Even consistent paint at crosswalks is not provided with many intersections having no crosswalk lines or only crosswalk lines in 1 direction.

Its fine in a few more year it will be to hot to even walk so why have side walks /s