Because you cannot deploy any media (data plane) functions on “K8s hosted on the cloud” i.e. worker nodes running as VMs.
Media functions are nothing but high-performance routers.
Examples of media or dataplane functions are -
𝗜𝗻 𝟰𝗚 - SBC, SGW, PGW, CGNAT, etc.
𝗜𝗻 𝟱𝗚 - UPF (User plane function).
All these data plane VNFs/CNFs require SRIOV (bypassing the hypervisor of the host server) for a telco-grade performance which you cannot achieve if your worker nodes are working as VMs on top of a cloud environment.
Rest all VNFs/CNFs are majorly signaling nodes & can be deployed either on cloud or on Baremetal also.