They’re in the position of authority and there is a chain of command, soldiers are trained from the very beginning to obey the chain of command without questions.
To climb the ladder or gain more power, they have to look good. They’re not going to get promoted if their records have any “negatives”.
Who is going to verify the reports? Their bosses, which means they also have the same incentives to only want good stuff, in order for themselves to get any considerations for promotions.
When their boss goes up, the boss under them will likely get promoted too.
What the boss said, goes. There are usually far more consequences toward the victims and whistleblowers than the actual authorities.
That’s why there should be independent review process where these folks have no incentive to have good reports.