Some historical background might be helpful: to configure network devices, the IETF specified SNMP in the 1990s. Cisco only did a read-only implementation of it

Some historical background might be helpful: to configure network devices, the IETF specified SNMP in the 1990s. Cisco only did a read-only implementation of it, as their configuration concept did not align with SNMP very well (a change of a single SNMP variable gets effective immediately, which is cumbersome in cases where several variables need to be changed in unison). So network operators resorted to 'expect' scripting of the routers' CLI, which was a brittle and ugly solution. Netconf/YANG was done to replace that.