It's natively supported by all of the GPUs listed, the trick is indeed bringing this to the consumer space for the first time as it has always been model locked and sometimes (e.g. Nvidia) license locked. The exception to these restrictions is with the Intel method.
Nvidia co-wrote the VFIO-Mdev API in partnership with Intel where it is used as a kernel interface for GVT-g mediated GPU devices (as well as Nvidia mediated devices). My (totally baseless) guess would be that Nvidia saw this market change coming with Intel ARC GPUs leaving vGPU functionality enabled across the consumer lineup and rather than getting left behind by a big change they helped bring it about. We're just exposing the capabilities of that API to the user across vendors and making it easy to interface with.