Buried in the article is the answer: "Apart from poverty and lack of lavatories, one of the reasons often cited to explain open defecation in India is the ingrained cultural norm making the practice socially accepted in some parts of the society."
It is part of the culture; eliminating public defecation will require eliminating that defective and primitive culture. Despite the hype at the end of the article, eliminating such a defecating and defective culture will require efforts spanning generations, not simply a decade.
Its not such much cultural as it is so much political, as no sanitary worker wants to clean anything and nothing can be done about it, their work being politicized. So even when public toilets are built, they become unusable within few months. You can build all the public sanitation facilities in the world, but if they can not get cleaned by cleaning staff or any sanitation standards be enforced because of politicization, there is no incentive for public sanitization. India will have to wait till new political regime that can overcome politicization of sanitation work.