Why can’t we replace MAC IDs with IP numbers?

Since almost all machines on the Internet have a unique IP address (setting aside network address translation and some others), why can’t we totally avoid media access control and simply use IP addressing all the way to the destination machine?

As most machines on the Internet have a unique IP address, why can’t we avoid media access control and use IP addressing all the way to the destination machine?

Because LAN hardware relies on data link layer communications for data delivery to destination machine.

Frames transmitted across a physical network must contain the hardware address of the destination. The IEEE 802 protocols for shared multi-access LANs divide the data link layer into a Logical Link Control layer that provides a way to address a station on a LAN, and a MAC layer that provides the interface to network media and frames data for transmission over the network.

TCP/IP sits on top of the LLC layer. IP addresses are virtual addresses in software that provide a network interface for applications to communicate across physical network implementations. There are no Internet protocols at the data link and physical layer. Internet protocols were designed for underlying network technology (see www.ietf.org/rfc).

TCP/IP provides the layer of abstraction for internetworking across physical network boundaries, but IP relies on the physical network to deliver data to destination machines.