content: If every vehicle is ... electric, you've just moved your bottleneck to the power grid.  But you end up with one supply chain's overhead to deal with, rather than a dozen supply chains for petroleum alone. You can make huge investments in the centralized generation end of electric power (improving "greenness", efficiency, changing what you use to generate it, whatever) without requiring slow adoption by consumers, while also taking advantage of the growing amount of local small scale generation through wind and solar. You can't make meaningful changes to the fuel (without killing off the vehicles) in the case of petroleum based fuels. With electricity, you can do whatever you want with however it is generated without impacting the delivered power. That would be attractive for a society moving forward technologically.