Because each church had its own needs. Remember the one truth: God provides for the needs of the church. For Rome, Paul mentions these. Are these the only ones? No. Are these all Rome will get? Doubt it. Paul is not trying to make a definite list from which to check off things. What he was stating is that there will be a variety of gifts because there are a variety of needs. In fact, what we find is that this is dynamic. There is an ebb and flow in life. At times we need strong motivation. Other times we need to just serve and provide. Other times we need to have a strong distribution of the Gospel. God provides for the needs of the church. He does it through people with gifts given by the Holy Spirit.
Think about it this way. My son plays certain games with his friends that have characters. These characters need to ‘level up’ if they are going to survive each round. He knows what his player needs and works to get those skills and talents to fulfill the objective. God knows what we need as a church because he knows what the future holds for us. So he is causing the movement of families and lives so that we can have the gifts, skills, and talents needed to move on to the next round. The job of leadership is to help everyone see where their skill set serves best. The job of the people is to serve and be sacrificial.