The Congressi India failed everywhere including convincing neighbours. Congress withdrew into a shell as regards foreign policy.A country of 1.2 billion people should not need to use force to allign a tiny neighbour of 23+ million people who are so close culturally and religiously in identity. A better question is what failed in making lanka a bhutan or nepal or even sikkim?
There has been drift all around. This drift will not be corrected in one day. Nobody has a magic wand. Every change takes time.
China has been on an "enticing spree" as it looks for projects to use its excess capital. India's neighbours are on the list of China. China can put up with low yielding or even loss-making projects as Chinese leaders do not face any accountability. Indian leaders are not in such comfortable position.
India and China will continue on two parallel paths. I doubt these paths will ever meet. Each country will decide what it likes. If a country likes India's culture and leadership, it will want to go with India.
I do not have a problem with any of India's neighbours not going with India. They are sovereign countries responsible for the good of their people.