This isn't about differences guys. Mark is a "stubborn" person and he stands by his decision and the reasons behind those. Most probably he doesn't want to revisit Dire Straits for the same reasons he took his solo career, beside he is old now and past his capability to play the way he played with DS, he most probably doesn't want to destroy his songs, his own creations, for the sake of some nostalgic reunion.
Don't picture him as some selfish egocentric spoiled old man, he is within his right to play or not. He has played thousands of times in front of fans when he felt he could deliver, there are so few musicians who can claim that have been on the road for the fans as Mark has been since day one. He is a lot more comfortable now with songs like Basil or Kingdome of gold or Ragpicker's dream or Privateer and so on.
Would have been it nice to see him play again with John, David and Pick? Maybe only to the satisfaction of seeing them together again, not to the playing itself. For example, I found nothing terrible with Led Zeppelin sitting in the hall when Stairway to Heaven was played on stage at their honoring on Kennedy awards 2012 I believe. On the contrary, you would feel satisfaction as an artist to see younger generation still playing your music.
Whatever his choice is, I will respect that, he has given so much to me through his music I can never repay. He has earned a free pass so to speak