Humans are tribalistic, like leaders who are assertive and charismatic, like simple answers, are easily swayed by emotions, fall victim to logical fallacies, and a plethora of other things that all work just fine if you're operating on a tribal level as we did for most of human history, or rather prehistory. Now that we are in a different phase of technological growth, which has brought with it massive social change, getting rid of all of that superstitious nonsense is very difficult because of aforementioned characteristics. What were beneficial as it tribal species, and arguably even after that, is now a liability. Or at least more of a hindrance to progress.

Because it's been the way it always has been, because people also hate change, are lazy, and tended to prefer both avoiding cognitive dissidents and minimizing effort to achieve desired results, getting rid of religion is a nightmare hassle. Even when the evidence is right there in front of them, people don't care. At least not enough of them. They'd rather listen to their authority figure, or do what all their friends are doing. Which if you're doing what all your friends are doing it just turns into a circle jerk. But since they're in that circle jerk, they tend to just stay in it, and because the people in it are their friends or family, they defend it because it's their tribe. We're kind of hardwired that way.

TLDR, people are dumb monkeys.