I think that you can find many reasons for this. I would say that Gandhi's title as "father of the nation" is because he had a vision for how the nation of India should function. He provided the template for a political and spiritual vision of the nation. Just as a parent should provide both physical and spiritual notions of the good to a child, Gandhi did this for his nation. While other leaders possessed conceptions of what India could be, Gandhi was able to posit a notion of the good where political freedom was sought after spiritual liberation. In this light, he sought to transform the nation and those who were in it. It is because of this that he is called "Father." He sought to give much more than a political ideal. Gandhi's methods of protest, stances on politics, and his entire state of being was based on spiritual elevation. It is in this that we see individuals flocking to both his ideas and his teachings, just as one would flock to a wise father.