To expand on this a little for anyone interested, the problem with classical market-making is that you only make money as long as the trades are crossing back and forth around a stationary price. If the market moves suddenly, you end up losing money. In your example, if a huge sell comes in at 10, and the market then moves down to 8 bid, 9 offered, the market maker has a position they bought at 10, but can only sell at 9 at best.

So, profitability depends on the ratio of the nice "random crossing" to the nasty "toxic flow". The toxic flow tends to come from large, well-informed market participants who can act very quickly. That means institutional players with colocated trading machines and so on. There are none of those on retail brokerages, so retail flow has a great ratio of random crossing to toxic flow, and so market makers are happy to pay for it. Meanwhile, the exchange itself is crowded with players like that, and there's a worse ratio, so market makers are a lot more wary.

This is why market makers invest a lot in low-latency trading. If you can find out about an impending market move, and cancel your resting orders before other participants cross into you, you can dodge the toxic flow, and have a better chance of making money.

Longer explanation: https://insights.deribit.com/market-research/toxic-flow-its-...

Unrelatedly, another source of revenue for market makers is maker-taker pricing, where the person crossing the market pays a little fee to the person who rested the order they crossed into:

https://www.investopedia.com/articles/active-trading/042414/...

But i'm not sure how common this is these days.