Why can my router management app show MAC when you say it's not possible?

Router management apps provided by router manufacturers get the MAC information from the router itself, not by scanning the network. This requires that you have admin rights to access the router's settings and that you enter this info into the management app. The management app then connects to the admin account and allows you to change your router's settings and see all the info the router has access to — which also includes the MACs of the connected devices.

Unfortunately, every router manufacturer uses its own proprietary closed-source interface to access the settings, so it isn't feasible to implement this in Network Analyzer. In any case, such functionality is only possible for a router for which you have admin rights, not for an arbitrary network you are connected to.