It seems to me that one of the bedrocks of Democratic victories in Presidential (and other state wide races as well) is that the San Francisco Bay Area is Democratic both in its urban core, and wealthier suburban outer areas. In most American urban areas we find a liberal urban core, such as Detroit, Chicago, St Louis, Houston whatever, but this heavily Democratic area is usually at least partially neutralized by a conservative suburban area so the overall vote count isn't so strongly Democratic.
With the exception of Houston, you picked really awful counterexamples
