Power has a lot to do with it.

On a small scale it's the power given to priests over their parishoners that is abused by the bad. In an ideal world, this power is supposed to be used to keep the weak parishoners on the straight and narrow, and to encourage the strong parishoners to use their strength for good. Fortunately, most priests are either good or, at worst, innocuous. The bad ones are criminals, and so are the members of the organisation who knowingly protect them.

The protectors are the religious descendants of the people who helped large numbers of Nazis to escape after the Second World War - because they were supposed to be anti-Communist.

On a large scale, there is the power over the individual conscience that Rome likes to wield because they have never worked out any other way to keep people true to the faith. I think many Catholics stay in the flock despite this, not because of it.