Some individual portions of Chicago are very walkable. Likewise with some small bits of San Diego, though you are right, not as good as European cities.
Gaslamp is a tourist area, you wouldn’t want to live there, there isn’t much around. It used to be really dodgy, no one sensible would go there, but they rehabilitated it to a significant extent. Unfortunately, it is mostly only frequented by 20-somethings getting drunk at the myriad bars and tourists.