It does not say that they were removed from their graves in Sefer Melachim, and not here!
Radak: Since the Navi said so, we know that it was fulfilled.
Why will they remove them from their graves?
Rashi (2): The Kasdim will dwell in the graves of the nobles while besieging Yerushalayim. They were beautiful like palaces 1 !
Radak (1-2): It was a punishment for them after their death. It says (36:30) that Yehoyakim's dead body will be "in the sun during the day and in the cold at night", and Posh'ei Yisrael will be cast "b'Chutzos Yerushalayim" (14:16). Chazal (Yevamos 63b) said that due to the sins of the living, the dead are removed from their graves - "the hand of Hashem will be upon you and your fathers" - is the digging up of graves. It asked, if so, how can it be that "death will be preferred to life" (verse 3)? If they dig up the dead due to the sins of the dead, this is their Kaparah - surely it is better than life! Rather, it is due to the sins of the living. The Gemara answered, death is better for Resha'im, lest they live and sin in this world, and fall to Gehinom.
Sanhedrin 96b: Amon and Mo'av were bad neighbors of Yerushalayim. They told Nebuchadnetzar to come to bring the Churban. He said, I will have no place to stay! They said, their graves (burial caves) are better than your palaces. You and your army can stay there!
