"Why does Nietzsche think that Christian morality or any objective moral systems hinder the progress of humanity?"

According to Nietzsche, the history of the West faced a very peculiar phenomenon that influenced all posterity: the advent of Christianity. From the moment that the Christian religion became institutionalized, a way of living and creating moral values came into force, geared to Christian teachings.

It is important to emphasize that Nietzsche, at no time, criticized Jesus Christ, but rather what they did of Christianity from the moment when the life of Jesus becomes a foundation for a religion, that is, from the apostles Paul, Peter and the foundation of the Catholic Church. Nietzsche asserted that Christianity, imperative from the Middle Ages onwards, imposed an inversion of moral values that would culminate in the weakening of the human being, as it is the negation of the moral impulses that speak louder in any animal. Controversial statements such as "Christianity is the revolt of everything that crawls on the ground against what is high" condense Nietzschean thought.

the minoan civilization flourished in the middle bronze age on the island of crete located in the eastern mediterranean from c. 2000 bce until c. 1500 bce. with their unique art and architecture, and the spread of their ideas through contact with other cultures across the aegean, the minoans made a significant contribution to the development of western european civilization as it is known today. labyrinth-like palace complexes, vivid frescoes depicting scenes such as bull-leaping and processions, fine gold jewelry, elegant stone vases, and pottery with vibrant decorations of marine life are all particular features of minoan crete.  

so basically their unique way of ding arts, as well as architecture.