Passing a TR is not as easy as some of the posters make it out to be. The pass rate is very far from 99%. It is an expensive thing for an airline to put a guy on a TR if he fails because he a) costs money on wasted training b) leaves a gap in the seat of the airplane which needs to be filled by another guy - one they now have to find yesterday.
So, you can see the bean counter's desire for maximum chance of the candidate's success. The best way to determine those criteria is another matter.
Naturally, you do not hear people boasting about a failed TR course, but it is not an uncommon phenomenon.