Not sure if that's the case - however doing V2L requires the manufacturer to add an inverter to the car, and making that powerful probably adds extra cost most customers wouldn't pay. TI just looked it up and my Ioniq can only do about 2kW sustained - but since this charges the house battery, that's enough - idle load is just a couple hundred watts.
If you have solar panels or time-of-use electrical rates, you charge the car when power is cheap/free, and spend stored power when the grid costs are high. During a protracted outage, maybe you drive the car to a fast charger.
You pointed out a significant limitation of my current setup - right now there are 2 plugs - one for discharging the car through a proprietary manufacturer's V2L adapter, and one for charging.
I'm planning to make a 'box' that can switch between the 2 functionalities on the same cable.
The whole setup is a bit clunky as it is right, now, but I'm kinda more surprised that it works at all, and how well the fundamentals work.
This whole thing was more of an experiment in 'no way you can do this' to actually doing it, but I think this is HUGE, and will transform the way people think about electric cars.
