In a regime like in North Korea, Kim Jong Un cannot show weakness.  To do so would be fatal
as those who support him may decide to off him and replace him with someone else. It is just
the nature of the beast.  This was the same for Saddam Hussein in Iraq who had to pretend that
he had weapons of mass destruction to appear strong to forestall his enemies within and without.
As far as these air force flights, it is not really a show of force as stated in the SA article.  These are
really practice drills  for the eventual real thing and to see how the North Korean
air defenses react and to determine where their radar sites are.  All very useful when the time comes.