From the biography of Cardinal Ratzinger:
“Prior to 2001, the primary responsibility for investigating allegations of sexual abuse and disciplining perpetrators rested with the individual dioceses. In 2001, Ratzinger convinced John Paul II to put the Congregation for the Doctrine of the Faith in charge of all investigations and policies surrounding sexual abuse in order to combat such abuse more efficiently.[145][146] According to John L. Allen, Jr., Ratzinger in the following years “acquired a familiarity with the contours of the problem that virtually no other figure in the Catholic Church can claim” and “driven by that encounter with what he would later refer to as ‘filth’ in the Church, Ratzinger seems to have undergone something of a ‘conversion experience’ throughout 2003 and 2004. From that point forward, he and his staff seemed driven by a convert’s zeal to clean up the mess”.[147] In his role as Head of the CDF, he “led important changes made in Church law: the inclusion in canon law of internet offences against children, the extension of child abuse offences to include the sexual abuse of all under 18, the case by case waiving of the statute of limitation and the establishment of a fast-track dismissal from the clerical state for offenders.”[148] As the Head of the CDF, Ratzinger developed a reputation for handling these cases. According to Charles J. Scicluna, a former prosecutor handling sexual abuse cases, “Cardinal Ratzinger displayed great wisdom and firmness in handling those cases, also demonstrating great courage in facing some of the most difficult and thorny cases, sine acceptione personarum (without exceptions)”.”
Prior to that it was mostly lay Catholics who tried to rid the church of homosexual priests. In many cases they were opposed by local priests and bishops.
Well, the drastic decline in abuse started in the late 70s. By the time the media got a hold of the scandal, both for the actual abuse and the cover up, it was 2002 and the instances of actual abuse were at the 40s and 50s level of reported abuse, before the sexual revolution.
I still think it was simply a decrease in gay men becoming priests for broader cultural reasons, apart from an discipline from Church authorities.
Freegards