Once industries transition away from tooling that uses gas/oil, there will be significant cost to re-tooling back to using oil or gas. At this point oil/gas losses value because there is a barrier to using it. If all cars on the road are electric cars, then oil refined into gasoline won't see much use and the price will drop (relative to the costs to harvest it). It's not like a rise in the price of electricity will send people with 100% electric cars running to the gas pump.