Earlier quoted context omitted.
This should be illegal if there is no way to contest/appeal.
It's the reverse. It's often illegal to divulge the content of a violation.
As far as I know, the reason no company divulges information like this is to stop the endless protests and appeals from people. Dealing with people who believe they've done nothing wrong even though they have is tiresome and expensive and the more information you give them, the more ammunition they have to protest.
The result is innocent people like (presumably) OP's husband getting shafted by a short email without any details, but it's finanicially unattractive to change the system so without court or legislative action I doubt Google will improve their services any time soon.