The pressure to get good grades in school causes many students to cheat on their homework and tests. If the student is not caught cheating, he or she may even get higher grades. But getting caught cheating may also result in being expelled out of school or university. Plus there are long term consequences of not learning and moral declines. It is a personal decision that one has to make on his or her own.
Parents are most likely be the top reason that many students cheat. If their child does not do well or reach a certain level of expectation, the parent may punish or ground the child. So the kid goes out of way and does cheating or finds other ways to achieve the level that he or she were to be expected from.