Why are the four Gospels different from each other?

Because they're four different accounts written for different audiences and purposes—not four attempts at an identical transcript.

Matthew writes with a Jewish audience in mind, often connecting Jesus to Old Testament prophecy. Mark moves quickly, emphasizing action. Luke, writing as a careful historian, addresses a wider non-Jewish audience. John, written later, focuses more on the theological meaning of what Jesus said and did.

Ancient biographies didn't work like modern journalism. Authors regularly selected, arranged, and summarized material to make a point, without that being considered dishonest. John even says directly that he's being selective—writing down enough for readers to believe, not everything Jesus did.

Differences in emphasis, order, or detail are what you'd expect from four independent accounts written for different purposes. Word-for-word identical Gospels would actually raise more suspicion of copying than confidence in reliability.