The linked article addresses this:
> Why was there a liquidity crunch in the first place? A crypto exchange is a weird sort of business, in many ways more like a brokerage than a traditional exchange.
> A lot of FTX’s business is in perpetual futures, a leveraged product, sometimes levered 20 to 1. If you are an exchange and you are in this sort of business, you will need to come up with the extra $100 to lend to your customer. Presumably that doesn’t come from your equity: You are doing some sort of borrowing, perhaps from other customers, [2] perhaps from outside financing sources, perhaps from your affiliated hedge fund, etc. You will have some customers who owe you money, and others whom you owe money. You will be like a bank. If everyone to whom you owe money demands their money back at once, you will need to get the money back from the ones who owe you money, which might be hard. (You might not have a contractual right to demand the money back right away, or it might be rude and bad for business, or you might have to liquidate them to get the money back and that would blow up the value of your collateral.) In broad strokes this is a reasonable description of what happened to Bear Stearns, a brokerage that financed its customers’ positions.
[2] (footnote in original article): Effectively a perpetual future involves you borrowing from and lending to your customer in offsetting ways: If the price goes up, you owe money to the long and the short owes money to you. If the short doesn’t pay you, then you still owe money to the long.