Now, stop and think about this for a minute. In the next situation, a man goes to confession, confesses that he abused someone, but now the priest becomes legally obligated to report this to the police and has to identify the person and exactly what he said. He may be even forced to be called on the witness stand. OK, once it is know known that the priest is obligated to, not only report said crime, but he also that he may be called on the witness stand to testify what was told him.
Question: Why would a person who's committed such a crime go to confession to begin with if (s)he know this would be reported to the authorities with the priest forming at least part of state's witness?
So, what we are left with is simply not one legal advantage for such an approach. But it's actually even worse than that.
If said person goes to confession, there must be a reason for that. The priest is not a washing machine whereas the person automatically walks out of the confessional brand-spanking new. Catholics are well aware of the fact that the church teaches that if (s)he is not truly contrite and/or has no intention of changing their ways, there simply is no absolution since the priest is merely the conduit, not the ultimate forgiver, according to Catholic theology.
Therefore, if the person goes to confession, something is clearly bothering them, and now the priest is in a position of giving advice, which may be to turn themselves in. Or maybe the person needs advice as to how to turn themselves around so they don't do what they did again. Etc.
The bottom line: There is simply no long-term advantage to forcing the priests to betray what has been confessed to them, plus there can be a long-term disadvantage because the priest is no longer in a position to help out anyone in that position of betraying confidentiality.