I believe this stems from a paper that came out about how some large percentage of PHEVs never plugged in. The large caveat was that a large amount of that data was from company vehicles for employees. Which those employees have very little incentive to actually plug in since typically the company pays for fuel costs.

There was a bunch of reporting on this study like this: https://cars.usnews.com/cars-trucks/features/phev-owners-not...

Here's the actual study (PDF): https://theicct.org/wp-content/uploads/2022/12/real-world-ph...

We may have talked about it on HN.

In plenty of countries those plug-in hybrids were sold with lots of up front subsidies and reduced running costs due to lower taxation for the first five years.