One, lots of the homes/condos out there now are empty. I’m not sure of the exact statistic, but i believe its between 20 and 30 percent. And there is a record amount of inventory for sale at the moment. So much of the so-called scarcity of housing is a side-effect of rampant speculation.
Two, San Diego has always been a desirable destination since its inception. This has not prevented previous housing slumps. Additionally, its not necessarily desirable for everyone! If you are interested in high-paying corporate jobs and/or affordable housing, its not a top pick.
Three, checking out the city vs. county of San Diego, its clear that most of the county is undeveloped.