Such a law wouldn’t increase reporting - there’s just a slight chance that some priests might end up in prison for having taken the confession of someone whose identity they were sure of. (Because this of course also covers the confessions of laity, not just clergy.)
Being granted absolution isn’t permission to go away & offend again - hence the traditional “go, & sin no more”. Asking for absolution with the intent of repeating a sin is a sin in & of itself, because you are neither truly penitent nor intending to reform. The Rite of Penance isn’t exactly a gripping read, but it does explain how it works. It is also possible, in certain circumstances, to deny absolution.
The IICSA Report on Child protection in religious organisations and settings (September 2021) is valuable reading - it includes a section on mandatory reporting, where concerns were raised that victims wouldn’t come forward if they knew the police would be informed. The Federation of Synagogues’ stance was:
we fear that requiring religious leaders to report these matters will have the unintended consequence of deterring complainants, victims and survivors from disclosing them to their religious leaders. If someone is not yet ready to go to the authorities, but needs to confide in their Rabbi, they will be reluctant to do so if they know the Rabbi is required by law to report their conversation. This closes off a route to pastoral care for the victim. It also means that the Rabbi may remain unaware of the situation in their community and will thus be unable to take measures to prevent the perpetrator from continuing to abuse, or to bring them to justice.
(Perhaps important to note that by contrast the respondent on behalf Liberal Judaism was FOR mandatory reporting; & indeed extending any such legislation to cover all staff & volunteers!)
That report was part of the work undertaken by the Independent Inquiry into Child Sexual Abuse, whose final report was published in October 2022. There are also multiple other small/specialised reports on their website. Obviously not easy reading, but important.