ESXi is... picky.
In practice the hardware compatibility list essentially means that it has been tested, and will definitely certainly work with that hardware configuration. If you are buying a licence - to some extent hardware support could be contingent on being supported
That does not mean that it will not run - it means that you could potentially have ...
In my case, it was because Hyper-V was enabled. I had it disabled in Windows Features but I was still getting the turtle icon in the bottom right of the VirtualBox guest window. To turn it off completely, I had to:
On the host computer, open Command Line (as Administrator).
Enter the following command:
bcdedit /set hypervisorlaunchtype off
Restart the host ...