Because Windows does not natively include drivers for every third-party Bluetooth chip. While generic Microsoft drivers might allow basic discovery, they often fail at audio streaming (A2DP), low-energy device pairing, or achieving the 5.0 standard’s 2x speed. You need the vendor-specific driver from TP-Link.
If you have a (e.g., T4U, T3U) plugged in, remove it temporarily while installing the UB500 driver—some older WiFi drivers conflict with Bluetooth installation. tp-link bluetooth 5.0 nano usb adapter driver download