Politicians are humans who knowingly choose to enter public office for the sake of exercising power, whether for altruistic or nefarious reasons (or some combination thereof).

The power is why politicians deserve greater scrutiny than the average person, and anyone who wants to keep their privacy intact can choose not to run for office. The loss of privacy (usually at the hands of the press) is already an implied cost of running for and holding office.

Not once they put themselves into the public sphere. They become chattel, bought and sold by special interests.