Usually, everyone does do that, which is why only hard-to-detect patterns remain profitable. Not something obvious like "buy options in the morning and sell in the evening" as in this example.

But maybe Jane Street only traded like this on some days, so you would need to know whether they had done so before you could hope to exploit them.

> Simply look at the market patterns and make a profit, duh! Why doesn't everyone do that?!

I know your question was sarcastic, but not everyone is able to see patterns. And not every trader is as good as the other. Hence winners and losers.