Why do people stop responding during a conversation?

This gets annoying and happens to me daily(mult times)I can't change something,if I'm not told what situation might be at other end.I'm usually very understanding.I don't if nothing said,if q or comment was liked/understood,or not seen.(That should help limit how many tries I do to see, if a response is coming,or not,b4 giving up.
FYI:Job isn't done just becauise 1 q was answwered!There are prob more.
Hope this helps?