To add to John's excellent post, there is also the additional factor of people "stocking up" in these circumstances (if you go out to fill the can for the Genny, it's common sense that you top up the car's tank at the same time, and keep it full because you're not confident of when you'll get the next opportunity), that puts an increased demand on the fuel supply logistics that in itself would cause problems even without the disruption to the electricity supply.

Modern economics means no company can afford to have spare capacity (fuel, tankers, drivers, etc) hanging around unused in case special circumstances might arise. If you try to do that, you're out of business before the emergency happens.

UK catters will remember the mad week earlier this year when rumours of tanker drivers' strike, aggravated by some stupid politicians were enough to get demand totally outstripping supply, in spite of no reduction whatever in the supply.