Because network function on iOS are very restricted (like not being able to display any MAC Address or have access to WiFi), these restrictions (or only a few) don’t apply to a Mac App.
So the Mac App shows of course MAC Addresses, includes a real WiFi scanner and even a Connections tool which had to be removed from the iOS App since iOS 10 is included.
Furthermore the Mac App takes advantage of the additional possibilities of a desktop computer with a mouse / touch-pad, a real keyboard and much more screen space. Details or content will be displayed in separate windows and you can show of course multiple of such windows so it is much easier to see many things at once or compare results.
For this reason, a complete separate App has been developed instead of just providing a simple Catalyst App which would have just made it possible to run the iOS App on a Mac.