In most human groups and individuals, there is a combination of reasons, and they vary. It is exciting to be a "brave new warrior of truth", or throw a rock at uppity people who think they are so smart. In some cases, just to have some friends and be somebody.
Whatever the reason, I am amazed at how obvious the motivated reasoning is and that it is impossible to get them to see themselves doing it. It does not bode well for the human race that people decide something and will grossly dismiss contrary evidence and conjure up impossible things to explain, all while a perfectly good explanation exists, confirmed daily in thousands of ways. To the point of ridiculous, unless you have a tribe to agree, then it's us against them, and logic, consistency, and rational thought are all impediments to winning.
The faith based system of thinking (decide first, then see only supporting evidence) is the same for FE, Q, stopthesteal, Trump, religion, etc) is a dangerous thing with modern tech. Internet and atomic bomb should not be accessible to tribal faith based people. Faith based concrete reasoning people want to win, abstract thinkers want to cooperate.
In any case, you can't win an argument with a faith based person. They have already decided. The rest is just bla bla bla. The sport of it for me is to force them into a ridiculous position, but they see it coming and just stop replying, change the subject, etc. The anger comes when you expect them to be reasonable and they aren't.