Why was Mohandas Gandhi shot

He was assassinated by a young Hindu who felt that M.K. Gandhi was more of a hindrance to India than an asset. He (Gandhi) supported the partition of India into a country for Hindus, Buddhists, Sikhs, Jains, etc. and one country for Muslims. He had also leveraged the Indian government to give the newly formed Pakistan monetary aid.

Nathuram Godse (the one responsible for the assassination) felt this was unjust, he being Hindu felt that someone whom most Hindus looked to for guidance should have a stance more lenient towards Hindus.

Some say that nationwide groups were involved in a conspiracy to assassinate him, but those groups have been acquitted of any charges.
Mohandas Gandhi was assassinated because the assassin (Nathuram Godse) believed Gandhi was responsible for weakening India by insisting upon a payment [55 crores rupees] to Pakistan.

The assassin (Godse) was a Hindu nationalist with links to the extremist Hindu Mahasabha.

Nathuram Godse and Narayan Apte bought a Beretta Semi-automatic firearm and went to Delhi on January 29, 1948. They checked into the Retiring room No. 6 at Delhi Railway Station. On January 30, 1948, at 5:17 p.m., Nathuram Godse shot Gandhi three times in his chest.