That’s because Californa lenders are subject to two regulations that work in favor of the borrower:
1. When pursuing any secured obligation like a home loan, they are required to try to collect from the colateral first, before going after the debtor; and
2. California has something known as the “One Action Rule”: when collecting a debt, you only get one shot at it (kind of like a “no-double-jeopardy” thing).

So how does that help the borrower? Well, most loans in California are secured with a Trust Deed, rather than a Mortgage. A Trust Deed allows the lender to foreclose on a house non-judicially, without going to court. This is much cheaper and faster that foreclosing judicially (in court), so it is inevitably what the lenders do. Foreclosing through the courts is slow and expensive, and unless the borrow has a TON of assets, it’s just not worth it. However, you can’t get a judgement through non-judicial foreclosure; you can only get the property.

So in order for the lender to get a deficiency judgment, they’d have to go to court.
BUT: here comes that pesky “one action” rule. Guess what? By foreclosing non-judicially, the lender has exhausted their one shot. Now they *can’t* go to court for a deficiency judgment!

The lend *could* of course, start out by foreclosing in court (judicial foreclosure), and then get a deficiency judgment as part of that proceeding after the foreclosure sale has occurred, but in practice it never happens.

There’s also outright ban on deficiency judgments in California when the loan is a “purchase-money loans”. Purchase-money loans (as opposed to a refinance) are non-recourse: you can’t go after the borrower, ever. You can only go after the collateral property (for 1-4 unit owner-occupied props).

For these reasons, deficiency judgments are effectively non-existent in California.