Different authors focus on different topics according to their interests, expertise, or target audience.
Matthew speaks of Jesus’ life in the context of fulfilling prophecies. His audience was mostly Jewish, and his intention was to show that Jesus was the promised in the Old Testament, fulfilling God’s promises.
Mark, on the other hand, was writing with a more Gentile (non-Jewish) audience in mind. His intention was to show Jesus’ desire to save everyone, inside and outside of Israel. Mark accomplishes this by paying more attention to specific occasions where Jesus ministered to the gentiles, affirming the church's ministry to the gentiles.