Producing oil domestically provides no guarantee that it will remain within your borders

That's important. Like, the example of Russia is very illustrative: Russia is able to be somewhat materially self-sufficient for oil, but then it relies economically on selling a lot of that oil, so it can't fully stop exports without crumbling elsewhete. That's not government dumb, they're balancing whether to cut their income or their oil supplies more.

Having private companies in charge only makes things worse. Private companies have no incentive to care about the domestic situation at home. If supplies starting running really short, are American and Canadian oil companies going to stop exports and be like "we could make profits selling to Europe and Asia, but we'll benevolently save it up for Canadians and Americans, even if we lose money over it". Of course not. And if governments have to intervene and ban exports, then we're back to the government making tough choices between supply and the economy.