Why does karaoke need a special audio system and why can’t I use the sound from the TV?

For technical reasons, the sound from the karaoke system is intentionally not transmitted to the TV speakers via the HDMI cable.

1. Firstly, due to the peculiarities of digital signal processing in the TV, there is a delay: you will see the image on the screen before you hear your voice from the speakers. It is simply impossible to sing with such a delay.
2. Secondly, the built-in speakers of TVs are not designed for the specifics of “live” vocals: they cannot cope with sharp peak loads and may simply fail.