There are multiple factors leading to high failure rates. Non-AQP programs, first time 121 training, a few gung ho examiners "keeping the standards up", and no incentive for the company to fix the problem due to slower attrition. I know Spirit tripped up a few people when their training was pretty poor years ago. The classes had 1 or 2 from each class fail the oral and then a checkride after 4 sims which failed another 1 or 2. Some groups had 10-20% of the class with failures by the end. Prior to AQP that really wasn't out of the ordinary at most regional airlines where people were seeing their first 121 program but to see it at a bigger airline was odd.