What is the reason for Karun Nair not playing in Indian Test team?

On December 19, 2016, Karun Nair created history. He played the innings of his career and became only the second Indian to slam a triple century in the purest format of the game. Thus joining the opener Virender Sehwag in an elite club .
Talking about his 303* , which came in the first innings of the final test of 2016 India/Eng series at Chennai was vastly appreciated including wishes from our honourable PM Narendra MODI .

After the series he was selected for series against Australlia where he could’nt make any impact and failed the tour drastically . His scores were like 26,0,23,5 in test matches against Australlia at Bengluru , Ranchi , Dharamshala respectively .

He just scored 300 runs in his 15 innings he played after his triple ton . Even his IPL performances were no eye catchers . I guess he just turned into a One Match Wonder. They could have backed him little more but there were better players on the rise like Mayank , also Vihari who was given a shot because of his bowling abilities . Moreover , India being so serious about cricket these things can happen and for being in the team just as a batsman you need to be at the top always .

Maybe some people will call our management baised but I don’t find any prejudice in his case .
As of just being 27 years old yet may he come back strong and better .