Is that 8.4 miles per day, or, 8.4 miles per journey?
Even with such short average journeys, it is quite possible a recharge would be necessary in the course of a day, if several short journeys were made.
The bottom line is, even for those who use their car for such short journeys, ICE is still more convenient, eg one visit to petrol station per month, vs (say) daily charging, (perhaps, at home, on your drive, for those who have that facility).
I recently changed my car. I did look very seriously at EV, but, decided on a hybrid, simply because IMHO the infrastructure is not quite there yet, and, in my price range, I feel the "development" phase in EVs has not stabilised yet, so, I felt the risk of it becoming rapidly obsolete was too great. Maybe, in 5 years or so, the scene will look different, and, I will go EV.
As an aside, I haven't noticed anyone state what is, to me, the obvious point, EVs are only "non-polluting" in fuel terms if the electricity to charge them has been produced by "renewables", burning millions of trees in Drax Power station is not environmentally friendly.