Tell me about Holi and why so many people in the world celebrate it?

Holi ( /ˈhoʊliː/) is a popular and significant Hindu festival celebrated as the Festival of Colours, Love and Spring. It celebrates the eternal and divine love of the god Radha and Krishna. Additionally, the day also signifies the triumph of good over evil,as it commemorates the victory of Vishnu as Narasimha Narayana over Hiranyakashipu. Holi is originated and is predominantly celebrated in the Indian subcontinent but has also spread to other regions of Asia and parts of the Western world through the Indian diaspora.

Holi is an festival celebrated by Hindus in India.  Even though it was originated by Hindu religion, it is celebrated across India irrespective of religion.  It has become a notable Indian cultural representation.  The reason so many people in the world celebrate it is because India has one of the largest population in the world.