Canada

It doesn't cut off interference at all, it just provides new targets who have less knowledge and awareness about the situation.

I think the bigger concern is that if there are other foreign influenced MPs who aren't listed in the report, then they and the country influencing them realize that CSIS/Canada doesn't know about them. Keeping it vague and uncertain makes it more likely that those people will be concerned and may reduce their interference to avoid detection.

Likewise, revealing which MPs are known to be influenced may reveal moles or informants that Canada has, thus curtailing future efforts at limiting foreign interference.

Or leave them there. Let foreign interference put effort into these people. Pull the rug right at/just before election.

Pull the rug now and there is time to turn more politicians.

That's not what "at the root" means. The guy selling himself and his country is the final part, the branch as it were. The root is the source of the money.

As for your reasoning, being able to further track intermediaries and see what else they have their fingers in is good security policy, as is sending back disinformation until such time as it becomes known the subject is compromised. Throwing these guys under the bus is usually the last step in the process.