The chips that were in the special Developer Transition Kit hardware that developers got over the summer did not support hardware virtualization, so there was no way for the Docker team to test. The M1 chip in the Macs shipping this week has that support, so the Docker team should be able to get things running soon.
Makes a lot of sense. There is no reason HyperKit would fallback to software virtualization when hardware support is not available because it's always been available for supported x86 Macs.