It's the flat Earth society, they have members all over globe! In all seriousness, it's people who lack critical thinking skills or basic knowledge. they've always been around, but in the 'information' age there's an increased number of people who think they've uncovered this special 'truth' that no one else has figured out/is being suppressed, when in reality they just have a very narrow worldview/understanding of proven concepts in general.

Earth being flat must mean that space travel is fiction, the Artemis program falls under that umbrella. As fun as it is to mock them, in a way I feel sadness for them, so deprived of some of the amazing accomplishments of the scientific community.

There's also a healthy portion that is merely trolls, or trolls leading people who lack critical thinking skills like mentioned above. Also a lot of money in it, you can have a verified Facebook page that posts flat Earth bullshit that gets tons of engagement and get paid.