You are misremembering the details of that cap. The $3k cap is for offsetting ordinary income. These people have little ordinary income. Almost all of their

You are misremembering the details of that cap. The $3k cap is for offsetting ordinary income. These people have little ordinary income. Almost all of their money would be from capital gains. A $1b capital loss can be used to completely offset a $1b capital gain and leave a tax bill of $0.