وَأَمَّا تَرْكُهُ فَلِمَانِعٍ مِنْهَا
Omitting the qualification is due to something preventing the intended increase of information.
A speaker may leave the object, location or time unspecified because it is unknown, immaterial to the listener, or unnecessary for establishing the action itself. Deliberate non-specification can therefore be rhetorically appropriate.
«أَكْرَمَ زَيْدٌ» establishes that Zayd honored someone. If the aim is to characterize his courteous action, specifying the recipient may be unnecessary. If the listener has asked whom he honored, omitting the object no longer meets the need.