I’ve never understood why intelligence oversight is the remit of the Prime Minister: historically, intelligence agencies in democratic countries tend to be the least competent and most corrupt sectors of the state, because their secrecy makes them less accountable than any other area of government. So you want to keep a close eye on them. But the Prime Minister is always going to be the busiest, most distracted member of Cabinet; traditionally our PMs have little experience in the portfolios that might be useful in running an intelligence agency (Justice, Foreign Affairs, Defense).
Australia’s intelligence agencies look like they come under the ambit of Foreign Affairs and the Attorney General. That makes a lot more sense.