If you pay $750k for a home and someone buys the highest parcel in the neighborhood (which used to be open park land), and puts up a shipping container that gets graffiti'd, your real estate value is going to take a hit. The neighborhood is now uglier, has less aesthetic quality, and is potentially endangered in case of earthquake.

Many cities have ordinances such that someone can't buy a lot in a neighborhood and turn it into a landfill such that everyone's property values suffer.

Cities have a complex web of zoning laws and construction permits for many, many reasons. Some of them are indeed health and safety related (fire codes, sewage transport to avoid disease outbreaks, making sure an industrial plant isn't manufacturing dangerous substances close to people's homes); some of them are aesthetic (making sure the neighborhood keeps a certain appeal); others are record keeping for future archival needs and dispute resolution (filed plans can be used years later to check the history of a property or verify the layout of it).

A city is a community that wants to protect community interests like not spreading disease and not irritating every single neighbor you have and keeping the continuity information of ownership and property history.

Local municipality code of ordinances. Land ownership does not convey unlimited rights.

“Unpermitted structures pose a safety risk,” City Attorney Mike Feuer said in a statement. “They also can be unsightly and erode the quality of life in a neighborhood.”

Basically, there are building and lot codes that are in place to protect neighboring real estate values against urban blight or non conformance to community standards.

Apparently, they're worried that the unsecured container would roll down the hill in the case of an earthquake.