I'm not sure how you figure that 400k/yr (dual-income) doesn't let you buy a 2m house, putting aside the question of why you'd want to - there are multiple listings under 1.5m in "safe neighborhoods" less than a 20 minute drive away from MTV, and yes, they have 2-car garages.
You're probably looking at a TCO of ~11k/month (mortgage, tax, & maintenance, and it's really more like 9.5-10k/mo after the mortgage interest tax deduction), which is arguably an unwisely large % of your ~20k post-tax take-home, assuming you're putting away a substantial amount into 401ks, but you're left with 9-10k/month, which means you can put easily waste whatever you want on luxury cars (as if you can't be "very comfortable" leasing a new Japanese sedan for under $300/month instead of lighting money on fire for the pleasure of driving less reliable vehicles).
But, I mean, you _could_ if you really wanted to. And still have enough money to travel internationally twice a year. And outsource whatever percentage of your cooking you want to takeout. I'm glad you agree that a full-time nanny would be stretching the definition of "very comfortable", and private schools seem superfluous if you're buying expensive real estate, since part of what it buys you is a spot in the local public school, and if you don't want that you can relatively trivially arbitrage it away by buying a cheaper house in a different zip code.
Is it possible that those people are making the arguably sensible decision to rent instead of buying, because the price to rent ratio in the Bay is truly absurd, and not everybody cares enough about "ownership" to spend an extra 20-30k/yr on it? That doesn't mean that they couldn't make the finances work if they had to, they just have... different priorities. Like putting an extra 20-30k/yr into the market.