Fuel duties help to offset the negative externalities to society of driving, namely CO2 emissions, pollution and congestion. With EVs tou don’t have emissions and pollutions and the health problems they bring so there’s no negatives to offset (ie fuel duty revenue will go down, but so will spending on health and environmental related issues)
There’s still the congestion any vehicle can cause and I think we’ll move to a much different form of vehicle taxation over the next 20 years, perhaps with more toll roads or even surge pricing style taxation for usage of roads.