Governments are democratically elected. Facebook is not.

You've used democratically in a positive sense in which I would contest. I don't think it's a force for good and in many cases it has ended horribly. A company is "elected" in the sense that they have to generate revenue (people have to willingly give them money in order to function). The same cannot be said for governments who forcibly extract resources from the people living within their geographic region. One is voluntary and one is forced. We are hiding under the guise of ethically contentious concepts like "social contracts" in order to justify the use of force as a proper mode of operation. Facebook hasn't murdered millions upon millions of people in their name, but governments have.

And how is a corporation better? A corporation is made with the ultimate purpose of making money for their shareholders. The wellness of the customers is not a goal at all.

Also, I disagree with the part about a corporation being "elected". If you don't like how your schools run, for example, you can vote for a different government, and at no point you will lose the schools for voting differently. If you don't like how Facebook is run (or any other company for that matter) the only way to "vote" is to be ready to stop using Facebook. In other words, the cost of having a say in how a company is running a service is possibly losing access to the service, and therefore the company has far more power over you than the one a "government" would have running the same service.

Improve them how? Also, if they become more powerful than governments, they don't have to answer to no one. Once they control your livelihood, you wouldn't be able to even complain. It's basically putting them at the doors of an authoritarian government.