The confessional is one of the world’s most productive intelligence-gathering systems. And it wasn’t part of the earliest forms of Christianity-- there’s no evidence it was used prior to Constantine. Even when it was first introduced, it was more of an annual thing connected to Lent.

The modern system grew in the middle ages because of its revenue-generating possibilities: the confession -> penance -> absolution pipeline included the possibliity of gaining forgiveness by donating large sums to the Church (remember indulgences?). Nice little earner, that. And it remains a rich source of material to blackmail Catholics who would otherwise do things that are inconvenient to the church hierarchy.

I’ve phrased this in such a way as to make it clear that it’s not just about pedophilia. The Church commits other crimes too (remember the financial entanglement with the Mafia that was exposed during the Banco Ambrosiano scandal?) and also seeks (and uses) other forms of political leverage to protect and expand its power. And they don’t want to be scrutinized for fraud or influence-peddling any more than they do for protecting pedos.