Let's flip it. Why do people want data on you? why are people willing to pay for it? or governments deploy threats of fines (backed up by men with guns) or men with guns in order to force it's collection on you?

private companies feel like they can make money with it, that they can make you do things that are profitable (buy something you wouldn't, vote a certain way, decide against insuring you etc). Are you cleverer than teams of academics? I'm not.

Governments want it to enhance control. Sometimes that control can be benevolent but it's still control. Often it's not benevolent, selective enforcement of unjust laws against political opponents etc.

So why surrender privacy?