What causes a complete removal of a poster and also all his posts ?

In the Real World Issues section, happened to a few posters.

And it left behind dangling references to his posts if someone earlier quoted in the replies.

Don't bother to answer if that is a top secret. Just curious if there is a disclosable reason.

I think if the person constantly post dangerous content it's easier to just wipe their existence rather than manually find the post and remove one by one.

there were some posters who got caught up with a bug on our code some months back. However, we were not able to identify all of them to get the action reversed. If you know who these posters are, let us know and we will review if their posts was affected and retrieve the posts back.

One probably happened a few months back and one just a week ago or less.

Not bothered with system bugs issues. My question is more like is there a violation of forum rule which is serious enough that warrants a complete removal of his account and all his posts ? If yes, what is the violation ?

Or it is like one poster says, too many dangerous posts, too difficult to remove them one by one, may as well completely remove the user and his posts ?