There are two or three different reasons.
The first is that it allows CSE or the Cyber Centre to take action.
The problem is that many of the critical sectors are targeted by state-level actors, and I've got news for you: If someone swipes in with a military badge on the other side and goes after a civilian structure, they're going to get in.
You can take a briefing from CSE on this: Adversarial states are loading up our critical infrastructure with malware. They are pre-positioning in the case of a conflict. That's bad. To the extent that we can increase the efficacy of government agencies on those networks, we should, against when something bad happens.
The second point is that it increases visibility across the network.
Third, it allows for the spreading of best practices. If there's an exploit that's used, let's make sure it only gets used once.