BCCI’s unstated policy to favour youngsters : BCCI, in recent times, especially from the Dhoni’s era, started to focus on youngsters. So, Gambhir, a 56 Test veteran, was overlooked along with Virender Sehwag, who after spending two frustrating years, retired from the game.
Even though Dhawan and Rohit are not in good form, BCCI selectors are averse to rock the boat and disrupt a largely steady team.
Besides this, BCCI never treats veteran players in a good manner as has been the case traditionally. These things happen to many players and Gambhir is just a new inclusion in this list.