Conspiracy theorists filter out anything that doesn't align with their theory and go to extremes to support their world views. E.g. flat earthers believe that all airline pilots are part of the conspiracy to hide the fact that the earth is flat. The scientific process, to contrast, would drive you to try and falsify your theory via experimentation, and the flat earth theory is so easily falsifiable.
If you look at vaccines, or climates, or 9/11, or those guys that believe nobody was killed in some massacre, they all use the same sort of logic (or shall we say non-logic). Despite overwhelming evidence they stick to their version of "reality", they never seek counter-evidence, they believe everyone but them is part of a ploy to hide the real reality from everyone. They don't trust experts or scientists.
It's not impossible to have conspiracies in the real world. But I'd say those are rare. The more people are involved the harder it is to keep a secret. There are also situations where the evidence isn't necessarily pointing overwhelmingly one way or another, and there is science that later gets refined or even overturned as more data/knowledge is acquired. Science isn't necessarily absolute truth, it's just the model that best explains the observable phenomena.