Because there's no evidence of anything paranormal. There's evidence for the basis of all theoretical physics.
If a scientist were to claim to me that they had travelled through time, but failed to produce any evidence, I would ignore them. If a scientist claims the inflationary theory of the universe exists, using data showing how celestial bodies are moving away from one another constantly, based upon red shifting, I'm going to lend credence to their claims. I can see it for myself.
You can provide no demonstrable, first hand evidence of the paranormal that I am able to analyse and assess, whereas I am able to do that first hand with all scientific theory, should I choose to.