Demographic data can be inferred from usage data. And if you're in a demographic that is currently being persecuted by certain lawmakers, that is a dangerous situation.

There was a time when Target outed a young woman as pregnant to her dad because of her shopping habits, Google would be able to know that just as much or more. For a current events example, someone searching for abortion access in a restricted state could be at risk of that data being used against them.

For a more direct situation, predatory advertisements would be able to pick out vulnerable people from the tracked data, and exclusively target them, like a payday loan agency only targeting those already deep in debt.