Like all members of the Roman Catholic clergy they have pledged themselves to obeying those above them in the hierarchy. Therefore, if they want to remain in good standing with Church authorities they seek permission from the Vatican to go.
And sometimes they get it. And sometimes they get the assurance that their departure is neither appropriate nor desirable.
https://www.belfasttelegraph.co.uk/opinion/news-analysis/malachi-odoherty-all-dioceses-must-now-come-clean-on-pervert-clerics-36660442.html
https://www.belfasttelegraph.co.uk/opinion/news-analysis/malachi-odoherty-all-dioceses-must-now-come-clean-on-pervert-clerics-36660442.html