Because, as has been reported over and over and over again, there is a almost universally accepted reality happening in San Francisco right now where wealthy Google (among other large tech companies) employees are moving into the city center, even though they work in the burbs, and driving up rents at an extreme rate. This is driving the previous lower income (lower than the Google type workers) home renting members of the community out.
Well yes and no. Missed the part about demand for the property increasing property values and making the original property owners, you know, the folks who actually own the land some nice pocket cash.
Sorry but this is just the way it is and the way it is supposed to be. These renters who are losing out to other people who have decided to buy these properties have no say in this matter. I am sure they are angry, but you have to ask yourself, if they were the ones with the cash wouldn't they be the ones buying the properties and not the google guys?