my best guess is that they don't see the price structure as maintainable, which will mean first deep price cuts which will then destroy the value underneath their loans - even those existing, which will increase the zone for people to just walk away, but will then also dry up the market ( as people wait ).

Better to call it quits then you can focus on wherever else.

They may not even have someone saying "this is gonna be a depression" - it might just be a series of economic indicators which they have a model run, and it says "yeah you're gonna lose 2% over the next 24 moths for every dollar you put in"