If there was indeed an explosive device on board, then it is likely to be similar to the one onboard Metrojet, which means quite simple device and not necessarily accurate.
Maybe it was just put there in Cairo and supposed to detonate after takeoff or later in that flight and just... didn't.
From a political standpoint I'd say that the impact for Egypt would be the same if the plane had crashed near France, given it is an Egyptian flight.
It would simply have added a political impact in France, just like metrojet which point was to destroy Egyptian tourism & to adress a political message to Russia. But again, endless speculation.