It's a habit to me but I think it's also a connection or acknowledgement of another human being even for a brief moment. It's probably habit for most folks but some truly are wishing you well. I've often thought about people and what their last interaction was with another human before they killed themselves. Would someone reaching out with a smile and a warm good morning or how are you have made a difference? Maybe or maybe not but it doesn't hurt. Just my own opinion.