To add a few other points to the list -
1. The pressure is also to literally survive, and can sometimes extend to their families. It's not uncommon to find Indian students coming to the US to alleviate their families' financial condition by studying here and consequently getting a job here. A lot of times their families would have mortgaged their apartments/houses to get a loan to fund the education. I was such a student about 3 years ago. If I would have failed, not only would my parents not have an apartment anymore, but it would also be difficult for us to survive as a family (my parents earn very little). I realize this was a calculated risk and no one forced me(us) into it, but it was very pressuring regardless.
2. While cheating is frowned upon at a run-of-the-mill Indian university, it's not dealt with as severely as at American universities. Consequently it can be a little like you were careless enough to be jaywalking in a foreign country you're visiting and finding out they're going to imprison you for it later.
3. The immigration rules here don't help as well. You have a limited amount of time for which you can stay in the US after finishing up studies to find a job. Failing to find a job in that time results into having to go back. Sometimes you have to go back even if you found a job but didn't get through the H1 lottery.
Let me firmly state that having said all of that, I don't condone this behavior, and am unreservedly against it. I'm just glad people here on HN already have additional perspective into why this happens and I'd just like to add to it since I feel I can.