>But can't energy from fossil fuels be generated in a decentralized manner too?

If you sit on an oil well, perhaps. In practice every static part of the production and distribution chain is a centralized target: from wells over refineries to depots, roads, harbours and finally power plants. You simply can't run fossils in a distributed local-first approach. That's also the reason why even for a massive oil producer like Russia, Ukraine can cause billions in damages with drones costing a couple hundred grand.