The graph seems related to the graph of venture funding over the same period:
https://en.wikipedia.org/wiki/File:US_VC_funding.png
Which is not surprising considering that salaries are the number one thing venture funding is spent on.
https://en.wikipedia.org/wiki/File:US_VC_funding.png
Which is not surprising considering that salaries are the number one thing venture funding is spent on.
Are you sure? I think that's possible, but my first guess would be rent (anywhere, not just in SF--unless you're all remote, even tiny corporate real estate is expensive), followed by salaries/benefits.
Regardless, it would be interesting to see some data explaining how VC funding is spent. Even better to see how the spending percentages change over time/stage.