The lesser extent of Nebuchadnezzar IV's rule compared to that of the preceding Nebuchadnezzar III probably accounts for why Darius thought it sufficient to send one of his generals instead of leading a campaign against the rebel himself.
Darius' choice to send a general instead of personally leading an attack on the rebel was influenced by the lesser extent of Nebuchadnezzar IV's rule compared to his predecessor, Nebuchadnezzar III.