Because it's super important for political reasons that San Francisco be seen as failing. It's the same phenomenon as perception of the national economy: if you don't like who's in power, you think the economy is poor.
7 of 9 offers were from Chinese nationals looking to park their money. Full cash, no inspection, no contingency and of course never visited by the potential buyer.
Market forces and demand are not necessarily about a desire to live there.
Or by counting the value of it's real estate. Or the value of the companies it has created.