For reference, the street view below is the heart of the Mission. Unfortunately, most people here would rather preserve the slums than build enough housing to support a diverse bunch of people.
https://www.google.com/maps/@37.765862,-122.419784,3a,75y,26...
On a relative per capita basis, SF is building a lot less than lets say houston or similar. And the reason why it's a lot slower is because of all of the above.
The developers are not entirely innocent since they always, without exception, ask for more than they are allowed, hence the endless reviews.
http://www.sfgate.com/opinion/openforum/article/How-San-Fran...
It took 6 long years with lots of fighting to try and develop a relatively modest 12 unit condo complex that met all zoning requirements.