@farmerman,
That is likely due to mainstream religions inability to admit imperfection in doctrine. When someone finds a flaw in a doctrine and can no longer accept it, he defects and a new religion is formed.
Its progression is similar to science, some continually look for the answers, never satisfied that they have them all, while others sit on what they have and declare themselves divinely correct.
One of these types will fly in the face of logic to cling to their established creed, while the other will adjust and correct himself whenever he is shown to be wrong.