VMware Workstation and Hyper-V – Working Together (techcommunity.microsoft.com)

They obviously care that you use and only use the solution they control, so their products, both through explicitly private apis and through undefined behavior, can have all the support they want while their competitors have to make do with the more limited public apis and unsupported behavior.

That way their product will always be better and more stable while they can claim to support competition.