Why do you not know what music sounded like before the middle ages?

It is not true that we do not know what music sounded like before the Middle Ages. While there are no surviving audio recordings from that era, scholars and musicians have been able to reconstruct the music of the time based on various sources, including written descriptions, musical notation, and archaeological evidence. There is a substantial body of knowledge and research on the history of music before the Middle Ages, and many performances and recordings of this music have been made.