Retail Licensing uses AVMA licenses to spin up your unlimited virtual machines which would need to be done through Hyper-V so that they can communicate with the host machine in order to activate. with ESXi, each container is ultimately independent of each other and there would be no way to ultimately communicate with the 'Host'. This would be why ESXi customers who are deploying their instances on separate containers would require the Open Value variation as it provides MAK or Mass Activation Key(s) which do not require communication with each other to activate. It simply requires an internet connection to ping to the Microsoft Servers.