Even if you find a new job and an affordable place to live -- not that easy to do -- you're going to have to pay a lot of out of pocket expenses (i.e. rental deposit, moving/packing expenses), which is really tough when 47% of American's are so cash strapped they can't afford to pay for a $400 emergency. [0]
It also has a high social and emotional strain. You'd be leaving all your family, friends, and cultural identify you've built up in a city. Plus if you're in a relationship or have a family, your partner would need to find work too, and your children would have to leave school/their social circles.
It's a really disruptive life change, and though sometimes it can help improve someone's financial situation, it's a tough thing to expect of thousands of people. I can't blame them if choose to keep struggling to get by in their hometown.
[0] http://www.theatlantic.com/magazine/archive/2016/05/my-secre...
My whole idea is to make it so service workers don't want to live in SF or work there either, causing services to either just not be available, or to cost an absolute fortune, seriously degrading the quality-of-life for SF residents. If you make it so service workers just can't live there (without resorting to illegal overcrowded occupation like you mention here), I think they'd just go elsewhere.