It would put management in a rather awkward position, I'm assuming there is no suggestion that drivers have been working excessive hours? Imagine an accident did happen due to a driver falling asleep, and he had told management about it previously, the inevitable question would be why was he allowed to carry on driving.
Well quite. If a driver tells their manager that they fell asleep, then they should be stopped from driving - on full pay - while it's investigated. If a driver fallls asleep and doesn't report it, they should be dismissed immediately. If a manager is told that a driver has fallen asleep and hasn't stopped them from driving, or if a manager has not ensured that drivers know that they must report safety issues, or has let a culture develop where issues don't get reported due to fear of consequences, then they should be fired. Managers should know that public safety is their number one priority and that their continued employment depends on them getting this right.
This is all basic stuff for safety-critical jobs.
I do wonder how it compares to the culture within bus companies.