>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.

Right. I think the most optimistic take would be that vegetable oil with some processing, can be used for diesel but I'm not sure how practical that is or how reliable access to waste vegetable oil is

Fair!