People get HELOCs now, intending to flip the house sometime soon. Suddenly the house depreciates substantially in value, they still have to pay for the HELOC and the mortgage for a house that they weren't planning on holding on to and can't get rid of and now they are trapped.

I don’t know about what you have seen, but a lot of of banks are not even offering new HELOCs now.

Sounds unsustainable. If enough people do that maybe we'll see some affordable housing soon!