I don't want to minimize the plight or the testimony of these people, but there are also hundreds of thousands of people who say it's worth staying. I would also say that not all international students come here to stay. You only have to think of the cabinet members who went to Oxford. They didn't go to study there with the intention of living in England. They came back and became ministers or held other positions.
International students are highly coveted people. Canada is always a popular destination for them. Not everyone has to or wants to stay, but in some cases, there are also avenues for people to stay.
There are certainly establishments that aren't doing their job and are just filling their coffers, but there are others that are doing their job very well.