Because cloud is commoditized VMs and VMware doesn’t have an edge in managing cattle at scale.
Their bread and butter is in managing pets and cloud providers expressly don’t want to encourage people to bring their pets into the cloud because people get mad when a few get killed.
OpenStack with the KVM backend is better than VMware at multi-tenancy so there really isn’t much value for VMware to add even over open source state of the art IaaS.