SW Courtesy

What ever happened to online courtesy? One can have a conversation going then all the sudden they just stop replying to messages. They will read them but do not respond.
Some will say they are too busy, if that busy why read the messages. If busy, just send a message saying they are busy and will get back to you.
Some go silent if subject matter is not totally to their liking, if so just tell the person that and move on.
SW needs a busy status indicator that can be turned on if don't want to be bothered by others.