Could there be a legitimate reason? Sometimes corrupt officials are placed under surveillance to catch other corrupt officials. If you out them you lose your information source.
I'm not saying that's sufficient justification, just spitballing ideas.
It seems your suggestion is that people would fight to keep their past crimes secret? That's an interesting alternative view.
I do realize blackmail and bribery are not the same thing.
(Not stating any political ideas, just following through with the logic of this discussion)