Why can't Apple Watch unlock a hardwired Mac that can see other WiFi devices on my home network?

Why can't Apple Watch and my Mac communicate for unlock when they are on the same network? Why is WiFi necessary?

My Mac has a wired connection to my home network for performance reasons. It can access all devices it needs to that use WiFi to connect (printers, my phone, etc.).

But I cannot use Watch unlock with it unless I activate WiFi on the Mac (which is pointless and has its own complications).

I'm not interested in enabling WiFi on the Mac, just in understanding the rationale at a technical level.