This is particularly true of pen pals. A few months ago I decided to give it a try. I've had contact with about 15 people. At the moment I only write to two of them. Those who I've "cut off" are exactly as you said. I have a standard that I keep. I make sure to answer all of their questions, I react to what they say about their day, and I see to it that I ask them questions. I know that some people are lonelier than I am so I am tolerant but I do expect them to answer my questions. Not everyone is an extrovert and so they don't know how to talk about themselves. I can understand that. But if they don't respond to what I've written then I see no reason to continue writing.
You can get angry about it or you can turn it into a game. A sort of psychological game. You could ask your friend if she/he has ever had a similar experience with a taxi or uber driver. Or ask if she/he uses them at all. It the reply is "no" you ask why not. If you want to play a double gave you can copy one of her/his earlier posts - change a word here or there with synonyms - rearrange it, and send it as though it's your own. Give it a try and let me know the results.
Ps. A lot of people say, “Just checking in to see how you are doing”. Don’t forget that they probably want to tell you how they are doing too. Do not misunderstand that. If you do not show any interest in them and their lives they will lose interest in you. If you are struggling to find a starting point, just clicking a button on your internet device will show you the temperature in just any place on earth.
Good Lord, I wish you'd just pick one and settle down. 
