Having rewards in games is important to keep the game attractive and engaging (King and Delfabbro, 2009). Having rewards such as extra lives and the scoring system increases the motivation of the player, therefore, increasing time spent on the game (King and Delfabbro, 2009). This reward system also means that the player gets a sense of satisfaction from spending time on the game as they feel they are being recognised for their achievements (King and Delfabbro, 2009).
King, D.L. and Delfabbro, P., 2009. Understanding and assisting excessive players of video games: A community psychology perspective. Australian Community Psychologist, 21(1), pp.62-74.