I don't understand why would EK want to trade-in some old A380's for new ones
Well, if they keep their business model, it makes certain sense. This because they need heavy metal and for the next 10-20 years, there are only the 380 and the 77X able to offer this capacity. So basically you have a choice of sticking to some dugongs, or to go entirely 77X, as a full 380 fleet would be a death sentence.
Changing some fuel guzzlers with newer models that guzzle slightly less, and having that sweetened by an almost suicidal offer from the manufacturer (thank you European taxpayer), would represent a keen move, at least for a mid-term fleet strategy. Macron's short visit must have helped, so let's wait for the last day of the (desp)air show for such an announcement.