To come back to the OP’s original question about canon law, I can make a few general observations that apply to law in general.
First, codes of laws need to be enforced. If you have a law on the books, but the authority in charge chooses to not enforce the law for some reason, then it’s going to be meaningless.
Authorities often choose not to enforce laws, or to selectively enforce laws, because they don’t want to admit that bad things are happening in their jurisdiction, or they don’t want a public record of bad things happening on their watch, or because they are protective of some person or group of people who would be badly affected by enforcement, or even because they are themselves guilty.
An example would be a police chief who knows he has a few corrupt cops but doesn’t want to bust them because he doesn’t want the newspapers reporting that corruption happened in his department, or because he himself has done some bad things in the past that he wants to cover up, or because he can’t believe that officers he knows as good people actually did corrupt things.
In some cases there are even legal loopholes to get out of enforcing certain laws.
Authorities will only enforce these types of internal laws when they either feel very strongly from a moral standpoint that it’s important to enforce them, even at the cost of bad publicity or losing some headcount, or else when the consequences of not enforcing are clearly going to be worse than the consequences of enforcing - such as huge money judgments against the institution, or a prison term for the chief in charge who didn’t enforce.
In any event, when a internal governance law is changed, it usually takes time and a few examples of what not to do, to change the internal culture of an organization. You don’t just see an overnight change with everybody suddenly accountable and doing the right thing. We are seeing this kind of internal culture change now in US dioceses as bishops, many of them older, are suffering consequences of past failures to report or address situations. Their successors going forward will likely be more careful because they saw what happened in the end to the past bishop who didn’t enforce, and they see the bad effects on their diocese in terms of eroded trust.
With respect to sexual abuse in particular, I’ve seen a whole lot of older people who just could not get their minds around the fact that somebody they thought of as an apparently decent person could also have this problem where they were abusing underage teens and children. Denial is a real thing. I’d say we only started getting past that as a society in about the last 20 years, partly because the older generation who were the biggest deniers has been dying off.