[brohee]

Because ultimately, stock prices move not based on "the market" but on things happening in the real world?

How does an algorithm interpret e.g. an Apple Keynote? By the time Twitter sentiment analysis (if such thing is really useful) gives results, an human trader already took a position...

[rezistik]

Humans are better at recognizing satire as well, April Fools jokes have famously caused some algorithms to react poorly.