What is the difference between UPF and Control NFs in 5GC?

During studying in 3GPP TS 23.502, I found the network functions services for only the control part or Control Plane (CP) of 5G Core network, However, the UPF or User part is separated (not exist as below figure). But Why?

5G Core Network Architecture

5G Core Network is based on SBA, The SBA architecture, fundamental in 5G’s move towards the claudication, is adopted by the control plane of 5G Core.
A network function (NF) constitutes of small service units called NF services (micro-services) and adding a new service will not impact existing ones, making scalability simple. where network functions (e.g. AMF) within the Control Plane enables other authorized network functions to access their services. So they communicate with each other through APIs or Application Programming Interfaces.

3GPP decided that 5G service exposure by the NEF should be based on RESTful APIs.

However, a User Plane or UPF, User Plane Function, is still based on the reference point model.