This is expected, Windows Portable Devices provides only a way to communicate with music players, storage devices, mobile phones, cameras, and many other types of connected devices.

It will not enumerate all devices on your system. Connect an IPhone and you will see pnp_device_id_count become 1.

To enumerate all devices you can use WinRT's Windows.Devices.Enumeration Namespace or the ancient Setup API.

Here is a (C# but you can do the same with C++) sample for using WinRT's one https://github.com/smourier/DeviceExplorer and a C++ sample for using Setup API: https://www.codeproject.com/Articles/14412/Enumerating-windows-device