The Network Control Protocols (IPCP, IPXCP, NBFCP, and Others)
Although PPP was originally created to carry IP datagrams, its designers realized that it could easily carry data from many types of network layer protocols, and that, on some networks, it might even be advantageous to let it carry datagrams from different layer 3 protocols simultaneously.
Allowing PPP to support multiple network layer protocols would require it to have knowledge of each one's idiosyncrasies. If you used only LCP for link configuration, the device would need to know all the unique requirements of each layer 3 protocol. This would also require you to update LCP constantly as new layer 3 protocols were defined and as new parameters were defined for existing ones.
To eliminate ...