For audio software like this, using a GC-free language translates into reliable, stutter-free, low-latency playback, particularly on lower-power devices. A lot of JavaScript-based audio things I've tried, even really simple ones, become miserable experiences once GC pauses start consuming a lot of CPU. I think it's no surprise that GC'd languages are unpopular for audio applications!
No, why would you? Normal OSes are pretty good at doing reliable audio playback and recording, musicians wouldn't use them otherwise. They don't guarantee five-nines but who cares. They are unlikely to ruin your audio experience.
