I suppose Dell already has a chunk of the server hardware space, makes sense to get into virtualisation since its a closely related industry and probably represents a big use-case for their hardware.
It also gets them into a "hybrid cloud OS", IaaS model...lines up well for competition with BYO Datacenter+OpenStack, or Windows 2016+Azure. VMware owns many, many assets beyond vSphere and has a strong chance (IMO) at becoming an incumbent hybrid SDDC provider with Virtustream, vCloud Air, VCloud Air networking, etc.
