Why do the armed forces propose to retain most Agniveers after 4 years of service?

Earlier former Army Chief Genral Upendra Dwivedi said any future refinements in the Agnipath scheme must be driven by operational requirements and real-world field experience, rather than predetermined targets or percentages.  

Why do the armed forces propose to retain most Agniveers after 4 years of service?
Earlier former Army Chief Genral Upendra Dwivedi said any future refinements in the Agnipath scheme must be driven by operational requirements and real-world field experience, rather than predetermined targets or percentages.