Because anti-trust. Companies answer to countries who don't like anti-competitive companies that aren't controlled by the state. People won't care but politicians will take notice of any company controlling almost all of their market which effectively gives them political leverage and dissatisfied voters. They also make for a great punching bag when politicians want to act like they are for the people because 100 million fine against Google means relatively little to google but a lot for getting voters to vote for you.