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Google knows that if they show the prompt people will sue them when they find Google has found other ways to track them, which Google WILL do. They'll have to, as it's how they make their money.
Sue on what grounds?

Read the TOS and understand that most consumers probably just blindly accept the TOS, preventing a lawsuit for such actions. Whether it be merely visiting a website or having data go through a proxy, these companies pay off politicians and judges to protect themselves.
 
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