Earlier quoted context omitted.
How are sidewalks "polish"? In most of the world, they're the default thing - before a roadway suitable for cars, before piped water, before sewers, before electricity.
Because where you gonna walk to? Your gonna walk 5 miles to Target and back? That'd why sidewalks is polish. Most sidewalks I see outside of tight downtowns are useless and barely used, and they aren't free to build and they don't generate anything if no one uses them...
The poor areas are super poor and semi-distant from goods and services. Biking somewhere from the poor areas, unless you have time and energy to spare, is going to be a big undertaking most of the time, not even accounting for the hills.