Why do people do that?

I haven't figured this one out.

I chat with people on line (who doesn't), but I've run across this phenomenon.

I've actually received and IM from someone that said "Hi", I said "Hello" back to them, and then they tell me "Can't chat now, can we chat later?"

Now.... If you contact ME and say "Hi", I assume that you want to chat. If you can't chat, then why do you IM someone in the first place?

Like I said, I haven't figured it out yet.....