Some sidewalks are actually meant for bicycle riding. This is a sidewalk, but it is also part of a multi-use path. It's a pretty good place to ride, only not too fast, or you might run over people.
Unfortunately, once you get past the multi-use path part, it turns into a regular sidewalk. Regular sidewalks are made for walking, not riding. Here's an example.
In my area, I think sidewalks are required when you develope land. But that also means it is okay for vacant lots not to have sidewalks. So you may have a mile of sidewalk and then it ends and then restarts.
The place where it ends and starts isn't always pretty.
Sometimes it just doesn't make any sense. This is a crosswalk. You can see the sidewalk in the background aligned with the power poles, and there's a sidewalk on the overpass behind me. But right here by the crosswalk, there isn't any sidewalk.
One of the problems with sidewalks is they like to jog them around obstacles. Which is okay if you notice in time. It wouldn't work so well on a road.
Sometimes, though, they don't bother trying to jog them around an obstacle. It's just right there.
(To be continued)