that's really not true. There are thousands of projects using e.g.

QtSerialPort (https://github.com/search?q=include+QSerialPort&type=code)

Qt3D (https://github.com/search?q=include+Qt3D&type=code)

QtWebSockets (https://github.com/search?q=include+Qt3D&type=code)

QtSensors (https://github.com/search?q=include+qtsensors&type=code)

Qt SCXML (https://github.com/search?q=include+qstatemachine&type=code)

etc etc..

Qt's value is as an app framework where you can assume interoperation across the same async runtime and enjoy a cohesive set of APIs for all your app's needs.