I mentioned Skinner Box before, I think it's time for a little explanation, just to show how it applies to some people in this thread.
The Skinner Box is operant conditioning. Operant conditioning is a very complex subject, but to break it down, it's teaching something (a rat, a human, a pigeon) to perform an action via rewards and punishments. There are three phases to operant conditioning.
First phase, Continuous: the behaviour you want is rewarded every time. You can't stay in this mode constantly, as your subject will learn it always gets a reward on performing the behaviour, and only perform said behaviour when it wants a reward. Rat pushes button, gets food.
Second phase, Intermittent: After your subject has learned behaviour=reward, you shift to this. You only reward the behaviour wanted once and awhile. This is where you want your subject to stay. The longer you keep your subject in this phase, the farther you can stretch out rewards. Rat pushes button 10 times, gets food.
Third phase, Extinction: If your behaviour/reward interval gets too big, your subject stops performing the behaviour. Falling into this phase is a failure.
Now, how does this apply to Elite? The people here complaining about "grinding" are operant conditioned. The behaviour is playing the game (grinding trade routes). The reward is a bigger ship. Early game is continuous phase, as they were getting rewards nice and fast. The "grind" phase is Intermittent. Now they have to "work" to get to the next reward, it's not an instant thing. Complaints about lack of "end game" content are the beginnings of Extinction. They're no longer getting rewards for performing the behaviour they were trained into.
The complaints about trade routes changing and such are a result of the depth of the conditioning. These people have been trained "Behaviour=reward". Anything obstructing the performance of the behaviour (trade routes changing) delays the reward state. The operant conditioned subject HATES delays to the reward state.
Elite honestly wasn't set up for this sort of Skinner Box behaviour. It's more of a "journey" game, where getting there is the reward. Sadly, operant conditioning is a powerful thing, and almost any system that has a set of "rewards" can fall into the trap. The nice thing is, once you realise you're in a skinner box, you can bust yourself out, and start enjoying the game as it was meant to be enjoyed.