Firstly, it is because of their writings. Sainath’s opinions are strongly backed up with facts and statistics. Arundhati generally paints pictures with words intended to jolt, shock and grab your attention. Sainath narrows his focus down to the details of one particular issue. Arundhati connects dots across space, time, history and continents, thereby creating a disparate mess of ideas.
Secondly, there is a clear difference between the topics they choose to write about. While Sainath consistently writes about rural India’s issues, Arundhati is here, there, anywhere and everywhere all at once. One moment she’s in Dantewada, the next at the Narmada dam, and then she’s off to Srinagar meeting the Kashmiri separatists.
Thirdly, it is the difference in their personalities. Sainath has received numerous awards which he has rejected. Arundhati, on the other hand is hungry for publicity - the very reason most Indians know Arundhati and not Sainath.
People who have read or known Sainath see him as an Indian, who criticizes the state as an honest concerned Indian. Arundhati, on the other hand owes no respect or love for her country. Her attacks are seen coming from an outsider. She has a more global perspective in mind, and writes more from an anarchist perspective.
It is still acceptable if someone sympathetic to the idea of an Indian state attacks it, but not when someone who seems detached to the idea of an Indian state itself attacks it.
And lastly, it is her sanctimonious tone which many (including myself) find disgusting. Her half-smile as she delivers speeches on the most serious issues is equally distasteful. She seems less concerned and more amused. Sainath on the other hand, prefers staying with the rural victims and does his bit to make their lives better.
And therefore, you ask a common man and he will tell you that Sainath attacks the government on agriculture and economic policies to bring in positive changes, while Arundhathi attacks the government on Kashmir, Maoists and Afzal Guru lurking for false publicity!
Sainath stands tall glorifying socialism in India. While every time the publicity hungry Arundhati opens her mouth, Marx and Engels would be turning in their graves.