They're blaming immigration and not the economy this time?
The driving factor is pretty obvious....
As a Canadian I am stumped, surely people don't like cold weather :)
Historically, when the economy is good US students have tended to defer business school because of the opportunity cost. For the business school, this was not an issue because they had international applicants clamoring for those spots.
So you need both -- a switch for domestic applicants (hot job market, tech jobs that don't require an MBA etc), and a dialing down of international applicants (harder to get visas, harder to stay etc).