VirtualBox and VMware Workstation (or VMware Player) is what we called an Hypervisor level 2.
Hyper-V or VMware ESXi are however Hypervisor level 1.
One of the main difference between the two sorts of hypervisor is the first is an application running inside an existing OS, while the latter is the OS itself.
It means that when you have enabled Hyper-V, your Windows 10 "host" became a virtual machine. A special one, but nonetheless a virtual machine.
So your question may be changed to: "Why VirtualBox and VMware Workstation does not work inside an Hyper-V virtual machine ?". One can answer because as a VM, the Intel VT-X instruction is no more accessible from your virtual machine, only the host can have it.
QEMU works because it does not do virtualization but emulation, which is completely different and explain why QEMU is awfully slow. Virtualization is the process to run a complete isolated machine inside another, but with the help of the processor. This requires the virtual machine and the host be instruction compatible.
The emulation is the process to run any machine inside a running OS, there is no platform restriction, it's why QEMU can run an ARM machine on an amd64 platform.
Note: QEMU has 2 operating mode:
- it can work as an emulator, this is this mode I explained above
- it can work as a virtualization software with the help of KVM if the guest architecture is compatible with the host's and if the VT instruction is present of course.