In Macbook, what are Thunderbolt MAC addresses for, if ethernet adapters provide ones? I think this answer and this one say that each ethernet adapter, such as USB-C-Gigabit Ethernet Adapter, has its own MAC address. So, that means Macbook (Pro) doesn't have a built-in ethernet card.

But I'm curious, what are the Thunderbolt MAC addresses then? In my MBP 13" (2015), networksetup -listallhardwareports command shows ethernet (MAC) addresses of Thunderbolt 1 and Thunderbolt 2. Also, the result of ifconfig -a contains bridge0 which has a MAC address.

What are they for, if every ethernet adapter decides the MAC address? Can I just ignore them?

Thank you.
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/