According to Young-Jin Lee at the University of Kansas, the main driver for college-level cheating is procrastination:
...repetitive copiers—students who copy over 30 percent of their homework problems—had enough knowledge, at least at the beginning of the semester. But they didn't put enough effort in. They didn't start their homework long enough ahead of time, as compared to noncopiers... Because repetitive copiers don't adequately learn...topics on which they copy the homework...copying caused declining performance...later in the semester.
This is partly our fault: we put students in an environment that seems designed to reduce productivity, then chastise them for trying to cope in ways we don't approve of. However, as I reminded a group of students this morning, how they respond to those pressures is still their choice: if someone says, "I had too much work from my other courses to do my part of this group assignment," they had better be able to explain why the other eight members of their team were able to manage it.