I have no idea how anyone can account for that. New light duty vehicle sales in the US fluctuate from 14-17 million vehicles a year. If you assume that realistically only 180 million light duty vehicles operate on a regular basis, that would mean that there would need to be about ~18 million EVs on the road to reach basically 10% of vehicles driven. I am not sure what the cumulative EV sales are in the US by now.
Yes, no direct account for that. But I would bet that asurvey of people that have both a BEV and an ICE would confirm what I said about BEVs being the primary use vehicle in a household. It would only make sense to drive the vehicle that would be more economical (and by far). Plus a BEV is so much convenient with charging at home vs having to fill up with gas. And also so much more fun and pleasurable to drive.
This web site seem to suggest there 4.8 million EVs and PHEVS on the road as of 2023. They say this about 2% of the vehicles on the road.
That data does not seem incorrect, but i wonder if they are knocking some off of the total cumulative sales from EVs being totaled, etc. Doesn't seem like it. I probably won't really trust any % of penetration number because I don't think there is a good way of knowing what the effective denominator is, unless you scoured all the insurance company data, which I don't think they would allow for good reason. (no sense in making everyone's personal data available to the whole public)