To offer my perspective on this, and feel free to disagree.
Corporations could (and do) use the data to increase profits - mostly through marketing and selling the data to marketers. While invasive of peoples' privacy - their freedoms remain intact.
Government could use the data for control, to maintain power over the people and could use it maliciously through imprisonment and maltreatment of people based entirely on the collected data. While also invasive of privacy - it has a risk of limiting freedoms or worse. People fear the possibility of this.
It's not that people necessarily trust corporations with their data (most users are simply unaware) - but rather that they have less to fear from companies than the government.
The government might revoke my drivers license because I show signs of road rage. The license being revoked could lose my transportation to work, losing my job. In the current economy and lack of job availability in my area - I'd lose my house. All over a little blob of data the government decided to use against me. Meanwhile, Google having that same information might show me ads for an anger management class.
I'd rather Google have it than the government in my contrived and made up example. I imagine that's why fewer people care if Google/Facebook know everything but want to keep that information from the government.
Privacy-concerned people use alternative-to-Google services like Duckduckgo and don't even have a Facebook. So they don't trust corporations either (although ironically turn to smaller corporations as alternatives?)