libvirt, virt-manager, et al are all perfectly suitable tools for an average member of the HN audience, or someone playing with a home lab, or any number of other technically proficient users - but those people are not the people who are buying vmware's products.

And virt-manager comes across from their docs as a bit on the basic side, proxmox and ovirt look a bit more polished - but again, companies are often wary of running their entire infrastructure on something where there isn't someone they can blame if it goes wrong - it's more about managing the risk than anything else.

I would absolutely love it if these sorts of companies used and relied on open source technologies more, but it's unlikely that they would pay for the staff with the relevant skills to manage it all, or pay enough to retain those staff that get trained up internally. (And I'm somewhat hopeful that this broadcom/vmware mess will cause more resources to flow into open source projects, or spark new developments in this space - cloud isn't always the answer to everything).