Apples to oranges. The bank's collateral is its lien on the house. A bank is not interested in foreclosing as long as you keep paying interest + principal ever

Apples to oranges. The bank's collateral is its lien on the house. A bank is not interested in foreclosing as long as you keep paying interest + principal every month. In fact, if the value of your house drops 90% it is in your interest to drop the keys off at the bank and say: "You guys can have it". A broker's collateral, when you buy on margin, is the security you bought. As the value drops, collateral goes towards 0. Of course they're going to cover their own a*. It's in the agreement you signed when you opened a margin account. Nobody changed any terms.