It's more a matter of "honor among thieves" kinda thing.  All these hierarchs have been storing away dirt on each other that they could then use as bargaining chips when the day comes they need to defend themselves.

I personally know of instances that then archbishop Levada refused to move against credibly accused priests because he feared about how they would in turn retaliate against Levada and the archdiocese.  Think about it like they have their hands at each others throat in a choke-hold.  Of course, in the Vatican and among clerics they call this kind of thing "fraternal correction."

Papa Francesco is faced with the conundrum that if he starts weeding out the problem curia and hierarchy members [think: Raymond Burke], he rightly fears the whole edifice of the church would start to collapse.

Anyway you look at it, Catholics are screwed.