Because it’s kind of awful if you don’t work in the entertainment industry? The public schools are crappy (which is a statewide issue), and the private schools are populated with the spawn of awful people. Public transit is half-assed, the traffic is unendurable if you have to commute during the long rush hours (thankfully, I don’t), the smog, while miles better than it was twenty years ago, is still pretty bad, and you really have to hunt around to find the culture tucked between the strip malls. With a few cultural exceptions, there’s nothing you could want in Los Angeles that you couldn’t find in San Diego, and enjoy a better standard of living to boot.
Of course, the not-too-distant future may hold the return of the NFL’s beloved Rams/Raiders/Chargers to Los Angeles, so whooptyfuckindoo for that.