Microphones in tvs are a useful accessibility feature when they enable voice commands for the user, and allow them to be used as voice assistants.
They also enable tvs with a camera and microphone to be used as video calling or audio calling interfaces. Used well we get star Trek view screens, used poorly we get little brother monitoring.
For those interested, it turns the tv into an interactive terminal for voice and camera powered video games, which are becoming more popular.
Unfortunately advertising and tracking incentives drive the abuse cases to the top and will crush the positive use cases :(