Ask HN: Why there is no app to convert your humming to instrumental?

I think a lot of people can hum a melody or entirely mimick how a instrument is being played all through their voice while learning to play a instrument takes a long time. Why isn't there any app which can do this? I like to think, I can mimick a melody played on a flute using my whistling technique but I find it weird that no app exists to achieve this.