Why Would Anyone Censor the Web?

I'm passionately interested in health, and I use the internet for research. While I don't consider all web info reliable, many studies and research articles are fine sources. I use a variety of search engines: Google, DuckDuckGo, Bing, Yandex, Brave, and Gibiru. I like to compare results on different search engines - and recently noticed huge differences! What's really happening there? I'm not sure yet, but my eyes are open, so I'm sharing it with you all. How would a search engine try to ...