My guess - and getting in Trump's brain is always a guess - is that he picked LA and SD because (a) he hates California, and (b) he's probably thinking about China, and (c) he thinks of those places as far away and not familiar to him the way New York and Miami are.
People are way overthinking this.
Why not a city in Texas or Florida? Was there a specific threat to the West Coast that he heard and is now "declassifying" because his brain is mush? Or is it another Mafia-like: "If Russia or China...has these emails, I'd love to see them."