Those startups should be hiring your developers at the rates they offer, and you should be paying those rates. But because the startups you mention think they need the CS equivalent of Einstein and Feynman to run their CRUD stack, your developers are ones they pass on (and then whine about a talent shortage), and allow you to pay the below-market rates you get away with, because in your segment of the market there is, apparently, an excess of labor available. Your description, in other words, isn't a counter to my point.
The bay area is expensive but I am proud that I can provide salaries substantially above the median household income in the US with decent benefits. How many people do you provide $65-95k a year jobs to? When was the last time you hired people who had been rejected by every other company they applied to because nobody was willing to look at their potential and take a chance? What percentage of community college graduates do you think make $65k a year to start? Heck what percentage of 21 year olds you even think make $50k a year? It's easy to criticize me and tell people who don't have 6 figure jobs that they're selling themselves short but hey talk is real cheap.
By the way a ton of the startups offering those 6 figure salaries don't earn enough profit to pay those salaries. Their investors are paying those salaries. What do you think is going to happen when the money runs out and there are no more sinking ships to jump to? Will you suggest that the unemployed engineers cling to their tulips?