Something that surprised me recently was learning that the U.S. Chamber of Commerce is a private organization. I assumed it was some office funded by the government in a town, that worked with local businesses—or something along those lines. But no, they're a lobbying group, and they are the biggest lobbying group in the country. I'm not saying they are a monster (I clearly don't know anything about them) but at that size, how could you not be?
https://www.opensecrets.org/federal-lobbying/top-spenders