Even in an insane place like SFO, a few high profile failures can shutdown the cash pipeline for all sorts of companies. No cash, no coders, no rent.
2008 proved that when people are underwater, they walk away from mortgages because they see no consequence.
For primary residences most are driven by loss aversion ("I'll sell it when it comes back to the price I paid for it, I don't want to lock in my losses, and this is still a decent place to live").
You're right that some markets experienced steeper declines than others, and the ones that descended quicker were highly leveraged through 0% down, or interest-only (or both) loans. Post-2008 lending scene has been much more restrictive, I can't imagine a lot of people being highly leveraged at the moment.
In the early to mid 00's the idea of "flipping" real estate became popular. The idea was that you would agree to buy a property, and then sell it very quickly, often setting up a deal to sell it before you even fully closed on it yourself. There were a lot of more-or-less amateur investor types who flocked to markets with cheap real estate and strong population growth - e.g. Las Vegas and Phoenix - and started flipping houses. This was pure speculation completely divorced from underlying demand.
I don't think there is anything like that happening today - at least not nearly on as large a scale. So, while I would disagree with the idea that "the market didn't collapse" - it did in some locations - I certainly do agree that it's not likely to collapse in quite as dramatic a way any time soon.