Same reason there is protection if you admit crimes to your lawyer and sometimes to your spouse. It’s a matter of privacy. It isn’t just some special club, any faith that establishes a rite similar to confession should be able to use a similar protective mechanism within certain limits to enable discussion about sensitive and possibly criminal issues.

Honestly I agree with you here. Either confessions are protected from being used as evidence or they aren’t there cannot be specific carve outs for this even for child abuse. Its all or nothing here.