Russian delay in delivering mission specific articles delay the commission and full operational capability.
Several item have to be sourced from Russia, most noticeably Mig-29K and the arrestor gear are delay due to Russian non-completion which in turn due to Western Sanction over Ukrainian intervention.
It took Russia 8 years to deliver the 16 Mig-29K India ordered for INS Vikramaditya in 2004, and due to the sanction they are unable to fill the 26 Mig-29K India ordered in the time frame, the time they need to bypass the sanction by setting up assembly line in India.
Also the carrier have system from everywhere, Propulsion is form the US, radar is from Israel, sensor is from Italy while weapon system is from India and Russia, it take time to put everything together. Hence the long operational readiness time.