There's also plenty of government regulations (at the local level, mainly involving zoning) that prevent building new housing, because existing homeowners want to keep property values high. How is that protecting peoples' safety?

Zoning is the least of your worries about keeping new housing from being built. There is an unwillingness to raze older buildings or industrial brownfields and turn them into housing. At least around here, there are many "undesirable" properties on bus lines, within reach of the city services, that would repurposed as housing sites.

There's an unwillingness because those aren't zoned for housing (or the kind of housing that developers want to build there).