Why did Christopher Columbus die as a criminal?

He did not die as a (convicted) criminal. He was by all contemporary accounts an extremely unpleasant man, greedy, pushy and very full of himself. He was also incapable of taking advice or of ever admitting he had been wrong about anything.
Although he was never formally convicted for it, he once was brought back in chains by the Spanish Government on accusations of instituting "a reign of terror" when he was Governor of the island of Hispaniola. He was without doubt guilty of mass torture, mass murder and theft of great amounts of gold and silver there.
He spent the remainder of his days completely convinced that wat he had found were islands off the coast of either India or Japan, and spent years of ligitation trying to get more money from the Spanish Government for his discoveries, without any success.