The mechanism is designed for asymmetric controlling and controlled stations (different message formats each way, session keys issued by the controlling station), message-oriented protocols needing per-message authentication, protocols without usable sequence numbers (so the mechanism carries its own), limited processing power (avoiding heavy public-key operations where possible), limited bandwidth down to 1,200 bit/s with per-octet charging (so authentication data is short), no access to an online authentication server, frame lengths of 255 octets or less, limited checksums, radio and dial-up media, many affected protocols with differing data link layers, remote sites and unreliable media.
The graph holds this control, the 0 it maps to, and the evidence behind each claim, over MCP and REST.