It's all of that, yes. But it's also:
* cost of living/price of housing per foot
* food costs are insane
* the culture is hostile to child rearing (even eg. Facebook offer bereavement leave and adoption assistance... but no on-premises childcare? That's standard for many large companies throughout the country.)
* the tax rate is obscene
* the tech work culture is extremely ageist, and anyone over 30 is going to encounter it
* the SF area IT culture actively encourages career instability (which is problematic if you'd ever like to buy a house).
You can make half as much in another locale and have twice the quality of living, if not more, in many other metro areas in the US, working in IT... if you're going to the bay area, you're likely in it to make a mark and a name, not to raise a family.