One natural solution would be to subsidize cyberdefense. The political difficulty is that a rational subsidy would be proportional to the harm of an attack, which would mean giving the most money to the biggest corporations.

The best solution would be for the firm to raise their prices the very small amount necessary to cover the expense, and for consumers to tolerate the expense because they know it's worth it. But a pipeline is a natural monopoly, presumably charging a monopoly-optimal price that (correctly) assumes a populace ignorant of such concerns until it's too late.

If a business externalizes the cost, does it matter to them?

Civil penalties levied by regulators will drive the change that matters.

I mean, yes? Maybe not before next quarter's revenue statement, but eventually it will have to start to matter?

If your dog goes and craps in the yard every day, you eventually have to clean it up or you will get flies in the yard, and if you have to open the door or leave the house at all then sooner or later you will have flies in the house, it matters, yes. It's really not any more complicated than that.

If you are responsible for dumping toxic waste out the back door of your factory, it's only a matter of time before it's in your drinking water at your house, a couple of miles down the road. Externalizing a problem doesn't really get rid of it, just makes it someone else's problem (for now at least.) Those other people are real people, and they will find you.