At the end of the day there is a whole industry out there making a living out of all this.
People go into panic when they see new questions being inserted into the bank - that will affect the results adversely - hassle all round
It all depends on how good one is at sucking out the content-, it all takes time though
Introducing a new syllabus often results in a high failure rate; of course they may be concerned that too many people are getting their pencil marks in the right place - after all its been a few years now since loads of people from the major schools were failing due to not having exposure to (what was then) the new question bank.
People bet bored after a while with the same old same old