Fundamental research is vital to our societies. We can discuss specific examples, but still it is never fair to ask what fundamental research will give in terms of practical applications. We just do not know yet, apart from looking back and realizing the past achievements. The truth of the matter is that curiosity is an essential feature of human culture. I remain convinced, and can provide a selected list of past and ongoing transformations for our societies. The most obvious and immediate are the computer and internet with which we communicate now.
To answer your question specifically : "what is the reason ?". It was not so much of a purpose rather than simply a choice or decision at a personal level to follow genuinely my passion. This is a selfish aspect, that not everyone wakes up in the morning with an urge to tackle the next step. But this aspect is merely incidental. I would go as far as claiming that if one has the ability and opportunity to pursue and contribute to fundamental research, it is their most important social responsibility to carry on. I can not imagine any better use of my life.