Who scored first triple century in the world in test cricket?

Andrew Sandham was the first cricketer in the world cricket who made first ever triple century in the test cricket. He was playing for England. He scored 325 runs playing against West Indies in 1930. It is wrong that it was his last match. He played later on many games for England. That period is very active in the case of world politics.
Your question of why a player not playing the cricket has many factors. Players performance, the performance of competitors, team requirements, etc. Sometimes the team has many options to select and the best have to select as per team requirement. The players you are asking about is Karun Kaladharan Nair played for India and scored a triple century after Virendra Sehwag. That was his maiden century converted into a triple. He is in Indian national cricket team and playing for India. Virendra Sehwag is not the part of the team India. He announced his retirement from international cricket. They played many matches after scoring a triple century.

Andrew Sandham (6 July 1890 – 20 April 1982) is the first cricketer who made the first triple century in test cricket. He was an English cricketer and a right-handed batsman. he played 14 Test matches between 1921 and 1930. He made the first triple century in Test cricket, 325 against the West Indies in 1930. He scored more than 40,000 first-class runs in his cricket career. Sandham broke a bone in his ankle in a motor accident in Durban in December 1930/31. That is why he couldn't play any test matches after the test in which he scored his triple century.
Virender Sehwag is the first Indian to score a triple century in Tests. He scored 309 runs in a historic test match against Pakistan in Multan. (March 2004). But he played many test matches after scoring his triple century.

Andrew Sandham was born on July 6, 1890 in Streatham, London. He died at an age of 91 on April 20, 1982 in Westminster, London. He was a right handed batsman and played for England, Surrey.

In 1930 he made the first Test triple-century playing a 10-hour innings of 325 at Kingston, Jamaica, when England accumulated 849 runs off the West Indies bowling.

Interestingly, he played many matches along with his opening partner Jack Hobbs who was more famous and earned cricket earnings more than him but most of the times it was Sandham who scored the runs while Hobbs failed miserably.

The first Test triple century was a made by Andy Sandham of England against West Indies in 1930 in the first Test series played in the West Indies and the most recent triple century was scored by Karun Nair of India against England in the year 2016.

It's not easy for a batsman to score a triple century in a test match. It needs lots of concentration, patience and stamina. There are few players like Brian Lara, Virender Sehwag, Chris Gayle, Sir Don Bradman who have done this more than once in the test matches.