"Is that at all relevant for the North American market, where no one would be using three phase power to charge their car?"
Most anyone in an industrial work setting in North America will have 3-phase 240V service installed, minimum. My work has 480V 3-phase for our SMT line. We have permanently-installed charge stations on that 3-phase service. Damn shame they've got nothing for my e-bike, so I just use the benchtop inside and a cable rig.
The benefit with 3-phase is that you now can use a single cable/charger to charge up to three separate cars, which greatly reduces the cost of setting up a lot of chargers in, say, a parking garage. And you can opportunistically deliver up to 11-22kW (240V/400V) to a single car. Greatly reduces the amount of hardware needed.
Plenty of chargers around where I live deliver 208v at 30a, which tells me they're connected to a pair of legs of a 3 phase circuit.
I suppose this means one leg of the circuit is not used, meaning the load between the different legs is always going to be out of balance, but this practice (use 2 legs of a 3 phase feed for "240 er... 208v" for "big" loads such as a drier or EVSE or water heater, so likely any industrial / commercial setting just accepts that you're not going to load up all legs your feeds evenly.
NA built EVs typically don't have the internal circuitry to manage 3 phase charging -- the EV takes care of the AC -> DC conversion on a level 2 circuit, and the extra stuff to do that in NA wouldn't ever be used. The same is true of charging off of 400v AC -- it's super rare and likely not something that's worth engineering to implement.
Most anyone in an industrial work setting in North America will have 3-phase 240V service installed, minimum. My work has 480V 3-phase for our SMT line. We have permanently-installed charge stations on that 3-phase service. Damn shame they've got nothing for my e-bike, so I just use the benchtop inside and a cable rig.