There's a trust that builds up between a creator and their audience. People start to comment when they start to get to know you as a person. This can be about commenting back when they leave comments, but there's also just a threshold of views before people say, "Hey, I think I know this person...I'll say something I know they'll react to (in whatever way they want...like it, consider it, whatever). You're a newer channel, so I expect this'll happen more and more often as your channel continues to grow and your audience grows to know you better.