Another reasons is that music makes it less awkward, most streamers aren't talking 100% of the time and there will be awkward silences. Also, for me at least, t

Another reasons is that music makes it less awkward, most streamers aren't talking 100% of the time and there will be awkward silences. Also, for me at least, the addition of music makes it more of a casual viewing experience. I'll often have a twitch stream on my second monitor while working and it's not distracting at all.