But they continue playing after the magical times of "just having fun" are over because of those "ego rewards". At least is what i think and what i do :S
You described exactly how i feel. But it doesn't necessarily lead to sadness...more of a feeling of "unfulfillment" and "quest of self improvement".
And the best part is once you reach your goal...you feel amazing and incredibly happy.
True, the game should be fun to play but after 10 years of playing a game one starts wondering...am i having fun purely from the gameplay and pressing buttons?
It's like my situation in League of Legends.
I have been playing that game for years! I know everything and have played all the characters. I burned out completely of it.
So what was my next step? Trying to reach rank Gold.
Do you know how much time it took me to reach that goal? 3 years!
That stupid ego reward made me dedicate myself to the game for 3 years after the phase of "just having fun".
Now i quit it because i am completely burned out.