The lack of innovation in payment technologies is a huge barrier. It should be entirely feasible to "set up a payment card" within a secure computing system like a car's computer (perhaps using an inexpensive commodity secure enclave processor), and then securely pay for charging services over an arbitrary wire protocol like NACS/CCS without the need to make an account for each provider. Apple and Google each managed to realize a similar functionality for NFC, but it took their enormous market power (and a huge mess of technical innovation that should have come from the payment card industry directly, rather than requiring still more proprietary systems.) In Europe they had to create an entirely new payment overlay called Plug & Charge, but it only handles that one application (and doesn't exist in the US.)

A good chunk of the problems in charging stem from the fact that we allowed basic infrastructure like payments to be locked up within these private companies, rather than mandating standards.