One reason: Almost half of their compensation packages are in Apple shares. So their lender, Opes Advisors, assigned the couple a financial adviser who used a software program to factor in debts and future income, including the stock, and the costs of education over the years for two young children.
They don't go into much detail, but this part scares me.
I'm assuming the "model" estimates some sort of future value for the stock. "You only make $150K, but don't worry, our model says that once your stock starts to vest, you'll be making $250K per year thereafter".
Of course that assumes their "model" of the stock price is correct.
However, California is a no-resource [edit:non-recourse] state, so if the owners get to the point where they can't afford payments, then it's the lender that is on the hook for the loss.