Yes this is true, and sometimes they don't even need to collect because they can write off the small loss (this is explained in the video from the webull ceo).
But the lenient margin requirements let them hang themselves when they can't collect because the losses are too big and will bankrupt the hedge fund. So now they are too big to fail, it's not only the hedge funds problem that they made a bad trade, it is now DTCC and the brokers problem that the hedge fund made a bad trade.
But the lenient margin requirements let them hang themselves when they can't collect because the losses are too big and will bankrupt the hedge fund. So now they are too big to fail, it's not only the hedge funds problem that they made a bad trade, it is now DTCC and the brokers problem that the hedge fund made a bad trade.