Security and stigmatization were two of the reasons, but so was the optics. Using huge facilities like the Olympic stadium and the Palais des Congrès gave the impression the numbers were huge and the government couldn't cope, while they were saying the reverse. Apparently they were only using a small part of those facilities.

As for "low skilled workers" on the one hand, and the assumption they have lots of money because they were working in the US and could afford taxis, etc.,isn't  that rather contradictory? If they were low skilled workers in the US, they were not making a lot of money, and good jobs or not,  they were likely living hand-to-mouth, and are now suddenly unemployed. How many middle-class Americans and Canadians could afford to lose their jobs overnight and then travel with their kids to another country?

And many Haitians are educated: teachers, nurses, etc.

http://montrealgazette.com/news/haitian-family-finds-sanctuary-in-empty-montreal-north-apartment