(...they still probably have a truth spell of some kind.)
She thinks sometimes by accident or because they tried not to but failed, but it might always be because they actually wanted to break the rule because of the inherent treachery or trying to do something else worse, and also they need to be taught and have it reinforced that they'd better not do it, so it's punished anyway.
Sometimes because they want to. They want to try secretly communicating with someone so they try it and things like that. (She does not mention running away here...)
Sometimes mages will say it was because they were upset - and that made them want to argue with a minder or destroy something and so on. That might always also be because of the inherent treachery.
Mages who are overly bad at following the correct rules are killed in childhood, but that still leaves everyone else. And they're taught a lot but that still doesn't do everything.
(Truth spells don't generally check for completeness. So she's not going to mention her co-field-mage who she's pretty sure has a habit of breaking minor rules to get minder attention on him and away from someone else. Or anything else in that vein.)
(She says things carefully and she keeps eyes on the ground and she shakes.)