[Theory] MAC Address … Networking?

I was thinking about the fundamentals of Networking, and it occurred to me that the purpose of a protocol like ARP is simply to find out what IP Address is assigned to a Host with MAC Address XX:XX…

This protocol literally seems to exist to help facilitation between Layer 2 and Layer 3.

I understand that we cannot in theory give every single Host in the world a unique IPv4 Address, but if every single MAC Address is unique in the world, why wasn’t Networking built upon Network communication (across the LAN/WAN/MAN) using MAC Addresses?

Is it simple because numbers are easier for machines to handle?