Did he do a great labor "El Tzor"?
Radak: It means Al Tzor.
What are "Mukrach" and "Merutah"?
Rashi: They are bald and peeled. Radak ? the skin on the shoulder peeled off due to carrying heavy burdens many days.
Who had bald heads and peeled shoulders, and why?
Rashi: Melech Bavel's soldiers. Those who besiege a city for many days, they toil carrying loads and rocks 1 (Radak ? on their heads and shoulders).
Malbim: The rocks are for the siege, and to shoot catapult rocks/
Why does it say that he had no reward?
Rashi: After he plundered it, the sea flooded (all the spoils went to the sea - refer to 27:27:4:1), for it was decreed that Tzor and its spoils perish in the sea.
Malbim: The verse depicts that Nebuchadnetzar was Hashem's Shali'ach and the staff of His anger to destroy the land. It is proper to reward him! They worked hard. A soldier's reward is spoils. The king's reward is to rule over the conquered nation, or if he destroys it, he is honored and feared. Neither received reward, for the sea destroyed it and washed away the spoils.
