In many cases is ignorance.
Ignorance is not only ignoring about something but is also learning things wrong.
An individual spent years of his life and lots of money learning the wrong theory. It will be very hard for him to accept another explanation for the same phenomena.
Others never review the reading and accept it just because comes from a respectable institution. Unfortunately respectable institution is not synonymous of being correct with its statements.
Our knowledge is second hand information because we ourselves can't test everything. Scientists themselves have the same experience. When the fraudulent news saying that Relativity prediction won against Newton's prediction by confirmation of the plaques from 1919 expeditions, no one of the scientists traveled to review such plaques. They just lean on the received letter and accepted them because came from a prestigious institution. However, the winning was because make ups made on the plaques. the winner in that test was Newton's prediction.
But, even when the information is not obtained directly from our own sources, the discussions are not vain but totally the contrary, these bring new ideas which might serve for other different approaches and discoveries.
