You need to take into account the skill of the player. You're registered since 2009, surely you have better PvE skills than someone who has been playing for a week. If we balanced the mission rewards around veterans, new players will hardly get much money out of it.
In addition, trading is a lot more relaxed than missions, especially for non-veterans. Discovery is one of the few games where I can do something relaxed while still making progress (by earning credits). Missions are cool, especially when you want something to do while you wait for the enemy to log, but I can't see myself doing them all the time to make credits - way too stressful.
