There's a whole industry of shady consultants and marketers pushing some of these things, including fake documents.
That doesn't excuse the federal government - they should've expected this.
I blame others like some of the provinces (who used international fees to avoid funding universities and colleges). And some of the colleges went WAY overboard expanding for international students and offering them fairly useless degrees (without building housing, too); some students bought into it because of the implicit promise of getting permanent residency status.
But again: the feds should have expected (they know from experience!) that fraud in the immigration system happens. They put the priority on more numbers and not checks and balances.
Plenty of blame to go around.