[RFC 7348] about VXLAN in the introduction says:
Data centers are often required to host multiple tenants, each with their own isolated network domain. Since it is not economical to realize this with dedicated infrastructure, network administrators opt to implement isolation over a shared network.
I imagine a rack with multiple servers, each one running multiple virtual machines(VMs). All VMs owned by a single server/tenant, compose its own isolated network domain? What is not economical to realize?