Bluetooth is 2.4GHz frequency band used widely to transfer audio and data. In many applications, where there is a Wi-Fi antenna it is shared with Bluetooth and dedicated Bluetooth antenna design is not needed.
However, there are many devices and sensors using low power version of Bluetooth (BLE) which benefits from higher antenna performance in terms of battery life. Another feature of Bluetooth antenna is price. Bluetooth devices are usually very price sensitive and benefit greatly from PCB trace solutions where BOM is driven to absolute minimum.
With introduction of Bluetooth 5 came mesh and long-range functionality. Mesh allows Bluetooth devices to connect to each other and create links forward. A great feature but mesh functionality does not have impact on the antenna design. The improved sensitivity and higher transmit power that enable longer range for Bluetooth 5 have an effect from antenna perspective. It creates another incentive like IoT antenna where range needs to be maximized and antenna needs to be optimal.