Every week there’s a new monster (MOTW) where all the evidence for outsiders disappears, or there’s the mythology where the government is covering it up.
I’m a huge skeptic in almost everything, but if I saw what she saw, I would clearly believe. That’s plenty of evidence for me, and I’m an actual scientist (well PhD engineer. I definitely did real science in school though)
The shit’s clearly real in their universe.
(Sorry, just been watching the first season of the x-files for the past few weeks)
The easiest answer is that the plot and themes required it. The same way horror movie victims do stupid things like splitting up or checking on noises in a dark basement. It’s necessary to advance the plot or maintain the status quo of the character relationships. Mulder needed a foil to his eagerness to embrace aliens and conspiracies as the explanation.