During the test series, they had all the star players representing them, including Rohit Sharma, Virat Kohli, Ravindra Jadeja, Ravichandran Ashwin and Mohammed Siraj. However for the ODI and T20I series, the selectors decided to rest several of players and opted to give chances to some of the bench players. And from what we can see, this hasn't worked out very well. Rather than directly inducting these players to the national team, it would have been better to first give them some match practice by selecting for the India A tours.
With Asia Cup,ODI World Cup ahead,BCCI rested their best players so that they don't suffer any injuries. The Indian team is well aware of the lack of players like Rohit Sharma,Kohli,Jadeja,Ashwin, Mohammad Siraj. That is why BCCI does not want to take any risk in the upcoming Asia Cup and ODI World Cup by resting them. All those who are playing in T20 series only play well in IPL and also in their own ground,I have not seen them play well with any team, I have not seen any memorable innings from them. I agree with you that they need to play well in India A team first. Will India find an alternative to batsmen like Rohit and Kohli? After their retirement BCCI will have to eat hard to prepare the future team of India.
T20 stars such as SKY and Ishan Kishan performs really well they play in India. It is an entirely different story once they play in surfaces that are not very flat, and against quality bowling attack. And one disadvantage with the young Indian players is that the BCCI prohibits them from taking part in franchise T20 leagues around the world. Therefore they are not very familiar with pitch and climatic conditions in countries such as West Indies. On the other hand, the West Indian players are very familiar with sub-continental conditions by now.