I think this has been becoming an epidemic with our phones and easy communication. I use to do this and was embarrassed of how I was conducting myself.
It is all just a pattern we create. Now I make certain that I always finish a conversation and always reach out to people to follow up with things. It is quite easy and you gain a ton more of respect from everyone.
I now see how bad it is because so many people do this to me. When we are in a conversation or there is something on going to talk about, people go away and do not finish it. Even after continuous follow up they do not. Some do after a long time of weeks or months.
It is not hard and does not take long at all to do this with a ton of people. It is only good for us.