Most journeys fall under 100miles
Which is not at all the same thing as saying that most cars are used exclusively for short journeys.
My daily commute is ~ 30 miles, but every month or so I do a 200-mile airport trip, and a couple of times a year I do 1000mile+ trips. If I had a car with a 100mile range, I'd need to buy a second one just for the long journeys, which would be both uneconomical and environmentally wasteful.
Ah! I hear the cries, just rent one when I need it. Not viable; most of those longer journeys are at weekends or holiday times, when everyone will want to hire long-distance cars. The only way to meet demand would be for the rental companies to keep huge fleets that lay idle most of the time, which would be both uneconomical and environmentally wasteful.
What about trains/planes? Drive my short-range car to the station, train to near my destination, rent a short-range car when I get there? Fails again, since it:
a) assumes I have a point-to-point journey to a single destination
b) costs a lot more
c) means I can only take luggage or other items that fit on a train/plane
d) all the other inconveniences like not having my choice of music, temperature, company, or the option to stop at interesting places on the way past, etc.
Short range electrics are really only useful as second cars, in households that can afford a main large car. These are unlikely to be the households that the taxpayer should be subsidsing with 5 grand off the electric runabout.
And don't forget that plug-in EVs are only cheaper because you're not paying the duty and tax on road fuel, the power they use is still probably coming from oil or gas in the first place. As soon as the fuel tax income drops significantly, the government will simply raise the same money from motorists in other ways, by road charging, or an annual electric car fee, or...