Look at the conversation again.
This time on the right you have a comment about why the form is simple or progressive.
Paul: Hello, John.  I haven't seen you for ages. 

Paul hasn't seen John at all - there's no sense of a continuous action.

What have you been doing since we last met? Paul wants to have lots of information about John's life - he is sure that a lot could have happened.
John: Oh, I'm still in Paris but I've given up my job You can only give up a job once and it doesn't take long!
and I've been studying at the Sorbonne since last October. John wants to make it clear that the studying is continuous, not just a one-time event.  He studies all the time.
John: Well, it hasn't been easy ... and it still isn't easy.  We don't use usually the progressive form with the verb 'to be'.
but my family have been helping me out John wants to make it clear that the family have helped more than once - it's a continuous process.
and Mary's been promoted. This happened just once - now she has a new job.
She's been working at the foreign desk since May. ... and she is still working there.  This is continuous.
 

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