A protocol built for a network that no longer exists

PPPoE was designed for the DSL and ATM era. When copper-fed DSLAMs aggregated subscribers over ATM virtual circuits, operators needed a way to carry point-to-point session semantics — authentication, per-user state, and accounting — across a shared medium that had no native concept of a subscriber. PPPoE answered that need by wrapping every subscriber's traffic in a PPP session, discovered and established through the familiar PADI/PADO/PADR/PADS handshake, then authenticated with PAP or CHAP and addressed through IPCP.

That machinery made sense when the access network was a dumb ATM cloud. It makes far less sense today. Modern access — GPON and XGS-PON, active Ethernet, DOCSIS 3.1 and DOCSIS 4.0, and fixed wireless — is Ethernet-native from the CPE to the edge. The subscriber is already identifiable at Layer 2 through the access node, the port, and VLAN tags. Re-imposing a point-to-point session protocol on top of an already-Ethernet network is solving a problem the network no longer has, and paying for the privilege.