He did not know the science of Sanjivini (giving life to the dead) which the greatly powerful Rishi (Shukra) knew very well. The celestial were, therefore, very sorry.
न हि वेद स तां विद्यां यां काव्यो वेत्ति वीर्यवान्। संजीविनी ततो देवा विषादमगमन् परम्॥