thunderbolt connection two Macs

Hello,

I've tried for about 30 minutes to connect two Macs with a new thunderbolt cable and USB-C->Thunderbolt adapter. Both of these are Apple made. They cost me close to $100.

I could have just done this with an ethernet cable by now, and I'm wondering why they charge so much for something that doesn't work right out of the box.

I have manually specified IP's; I have tried automatic DHCP. I have renewed lease. I have deleted the Thunderbolt interface and re-added it.

I have disabled all other internet connections along with these configurations.

I have used the same subnet with the manual IP. I have verified that the connection shows within System Profile on both systems. I have set internet connection sharing via thunderbolt connection on either one or both of the Macs.

I have rebooted both Macs.

Yet ... it still shows Thunderbolt bridge disconnected.

Why in the world, a hardware detected (on both sides) and a manually configured IP refuse to connect is beyond me. It worked fine with ethernet of course.

I also happen to work in IT. So I'm pretty good at troubleshooting.