Comment: You are right, the Church did not deal with this matter in a comprehensive way. I don't think there is a single reason for this. 

Although child sexual abuse (CSA) is and has been a widespread phenomenon both culturally and historically, civil society did not deal with it comprehensively until very recently either. 

The age to marry in the RCC according to CCL has been 14 for the longest time. So sexual contact with people fifteen and up could have been explained away as sexual misconduct/sin, and not abuse, that could be fixed by spiritual means (confession, prayer, etc). Remember,  the overwhelming cases of abuse involved postpubertal individuals.

Every institution has a basic reflex to protect itself. Add to this the fear and disdain of scandal in the RCC, and the high regard for the secrecy of the confessional, and you have a strong incentive to keep things private or secret.

These are just a few reasons, but none of this justifies anything. But it is worth considering them.