In Macbook, what are Thunderbolt MAC addresses for, if ethernet adapters provide ones?
You can connect two Thunderbolt-enabled Macs together using a Thunderbolt-to-Thunderbolt bridge connections, therefore you'd need each end to be able to identify itself.

More information here: https://9to5mac.com/2016/11/22/macbook-pro-thunderbolt-3-bridge-network-video/