I don't think that Golovkin is still that huge of a draw to just pay 4 million for a belt essentially. However, once he KOs a superstar he will then ascend into a household name. He was on the verge of it years ago with JCC jr, who later backed out of the fight.
I was hoping Andy Lee would retain his WBO belt because he was dead set on facing GGG. Unfortunately for GGG, he is currently int he same situation as prime Tyson where everyone was afraid of him and it was dificult to get fights. If you see a guy KO 32 guys and you are his 33rd opponent, what is in it for you? unless you can get some kind of huge monetary reward out of it.
It make sense that he is asking for 4m.