You can already do this trivially with Linux vcan[1] so I don't buy this argument.
I think the bigger factor is that innovation in the CAN ecosystem has been lagging behind Ethernet for decades now. Only reason it's had such staying power is industry inertia.
The relative cost is probably a factor (which overlaps with inertia of course, but if the thing you already have implemented is also cheaper, you aren't going to hurry up and change).