I live in Los Angeles and am lucky enough to rent on a street that is single family houses. It is illegal to build a duplex here, or a structure above 2 stories, even though each house must be 2500 sqft still.

People who are pro-market forces (such as myself) believe strongly that if you were allowed to build apartment buildings in neighborhoods like this that enough capital absolutely would be raised to raise supply. After all, you could take the current house I rent now and put in two walls for under 50k and start renting it out as a duplex two families but that is currently illegal. Hard to blame the market forces for this.