If the Dems hold their convention in San Francisco or Atlanta, that would be the equivalent of the GOP holding it in Moscow.
Why do people despise coastal Democrats now?
Bad rep. SF and California are already safely D, so it wouldn't win them any points holding it there.
Conventions don't win vote points anyway. Seriously, when has a state ever been flipped by the convention being held there? See 2012.
The real reason not to hold it in San Francisco is it's already expensive enough for delegates, putting it there would be a slap in the face to anyone without a trust fund.