Firstly: this is a city of transplants. You'd be hard-pressed to find a native SF'an in your daily interactions. (I know just a couple, and I've been here 6 years). As a result, many of them don't vote; or if they do, they don't have the context to see through the bullshit that is put out there. They'll take a politician's word, when a long-term resident will remember that that fucker has been lying for 20 years. As a corollary to this, you can control the City if you can put together a decent-sized voting block. So, for example: the City has 25,000 employees. If you can get the City employees on your side, then their votes alone are enough to swing most elections in your favor. For example: many years ago, the MUNI drivers got the City Charter amended to guarantee that they would be at least the second-highest paid drivers in the nation! Can you even imagine the clout they had to modify a city's constitution? (Thankfully, this was repealed a couple of years ago).
Secondly: the City has a lot of money to spend. The people in power stay in power via a huge game of doing (and getting) favors. For example: the City spends over $500 million/year on various "non profits". Your non-profit won't get a dollar unless you employ "consultants" who will help you write the proposal; and these consultants are very well-connected people. And they get a ton of money for a few days work (it's not uncommon to see such consultants be on payroll making $300K at a non-profit, but noone ever sees them at work).
Thirdly: the City is exceedingly corrupt. If you know the right people, you can get away with anything. This is why you have leeches like (Slick) Willie Brown and Rose Pak running the show. They know how the system works, and make a living just by greasing the wheels and pulling strings.
This is why, during elections, I vote for the people who are the most removed from the corridors of power. Anyone who has had anything to do with the System doesn't get my vote. It may be like throwing the baby out with the bathwater, but the City needs an enema.